1. A panchromatic sharpening method of spectral image based on fusion of overall structural information and spatial detail information, comprising: A) performing brightness linear stretching on a panchromatic image, so as to set the variance s P of the panchromatic image to be equal to the variance s S of a corresponding spectral image; B) respectively interpolating N components of the spectral image, thereby generating interpolation images I 1 , I 2 , K, I N having the same resolution as that of the panchromatic image; C) subtracting the interpolation images I 1 , I 2 , K, I N from the panchromatic image after said linear stretching, thereby obtaining difference images D 1 , D 2 , K, D N ; D) performing Gauss filtering on the difference images D 1 , D 2 , K, D N , thereby obtaining difference tendency images S 1 , S 2 , K, S N ; and E) respectively subtracting the difference tendency images S 1 , S 2 , K, S N from the panchromatic image after said linear stretching, thus obtaining fused images U 1 , U 2 , K, U N .