1. A color conversion method based on LCH color space, comprising the steps of: inputting source graphic data based on LCH three-dimensional color space; dividing color space having all colors corresponding to said source graphic data into n two-dimensional color spaces, H 1 , H 2 , H 3 ,. .. , Hn−1 and Hn, respectively, where n being a natural number; defining most saturated peripheral specific points of two-dimensional color space Hn having said source graphic data as An, Bn, Cn, Dn,. .. , and defining most saturated peripheral specific points of target two-dimensional color space Hn′ at same hue level as two-dimensional color space Hn having said source graphic data as An′, Bn′, Cn′, Dn′,. .. , where An′, Bn′, Cn′, Dn′,. .. , and An, Bn, Cn, Dn,. .. having a first-type one-to-one mapping relation; based on said first-type one-to-one mapping relation between said most saturated peripheral specific points An, Bn, Cn, Dn,. .. , of two-dimensional color space Hn having said source graphic data, and said most saturated peripheral specific points An′, Bn′, Cn′, Dn′,. .. , of target two-dimensional color space Hn′, determining a first conversion matrix; based on said first conversion matrix, converting two-dimensional color (C, L) of any most saturated peripheral specific point in two-dimensional color space Hn into two-dimensional color (C′, L′) of corresponding most saturated peripheral specific point in target two-dimensional color space Hn′; based on said first-type one-to-one mapping relation, determining a second-type one-to-one mapping relation between most saturated peripheral specific points An−1′, Bn−1′, Cn−1′, Dn−1′,. .. , in target two-dimensional color space Hn−1′ and most saturated peripheral specific points An−1, Bn−1, Cn−1, Dn−1,. .. , in two-dimensional color space Hn−1 having said source graphic data; based on said second-type mapping relation, determining a second conversion matrix; based on said second conversion matrix, converting two-dimensional color (C, L) of any most saturated peripheral specific point in two-dimensional color space Hn−1 into two-dimensional color (C′, L′) of corresponding most saturated peripheral specific point in target two-dimensional color space Hn−1′; based on said two-dimensional color (C, L) of said most saturated peripheral specific points An, Bn, Cn, Dn,. .. , of two-dimensional color space Hn and said two-dimensional color (C, L) of said most saturated peripheral specific points An−1, Bn−1, Cn−1, Dn−1,. .. , of two-dimensional color space Hn−1, computing two-dimensional color (C, L) of most saturated peripheral specific points Ax, Bx, Cx, Dx,. .. , of two-dimensional color space Hx at any hue level between two-dimensional color space Hn and two-dimensional color space Hn−1, where Ax=(C Ax , L Ax ), Bx=(C Bx , L BX ), Cx=(C Cx , L Cx ), Dx=(C Dx , L Dx ),. .. ; based on said two-dimensional color (C′, L′) of said most saturated peripheral specific points An′, Bn′, Cn′, Dn′,. .. , of two-dimensional color space Hn′ and said two-dimensional color (C′, L′) of said most saturated peripheral specific points An−1′, Bn−1′, Cn−1′, Dn−1′,. .. , of two-dimensional color space Hn−1′, computing two-dimensional color (C′, L′) of most saturated peripheral specific points Ax′, Bx′, Cx′, Dx′,. .. , of two-dimensional color space Hx′, having same hue level as two-dimensional color space Hx and between two-dimensional color space Hn′ and two-dimensional color space Hn−1′, where Ax′=(C Ax ′, L Ax ′), Bx′=(C Bx ′, L Bx ′), Cx′=(C Cx ′, L Cx ′), Dx′=(C Dx ′, L Dx ′),. .. ; based on said most saturated peripheral specific points Ax′, Bx′, Cx′, Dx′,. .. , of two-dimensional color space Hx′ and said most saturated peripheral specific points Ax, Bx, Cx, Dx,. .. , of two-dimensional color space Hx, computing a third conversion matrix between two-dimensional color (C*, L*) in two-dimensional color space Hx and two-dimensional color (C*′, L*′) in the target two-dimensional color space Hx′; through said third conversion matrix, computing target color converted from color of any point of said source graphic data in two-dimensional color space Hx; and outputting or preserving bull's eye chart data corresponding to said target color after above said color conversion.