1. A method for trademark retrieval, comprising: S 101 , establishing a sample trademark library and establishing a correlation between sample trademarks and division data for figurative element codes of known pending or registered figurative trademarks; S 102 , extracting and processing image feature information about the sample trademarks, and establishing a correlation between the sample trademarks and the extracted image feature information; S 103 , extracting and processing image feature information about a trademark to be retrieved; S 104 , taking the image feature information about the trademark to be retrieved as a retrieval condition to carry out matching retrieval, and finding out a sample trademark matching the image feature information about the trademark to be retrieved and reaching a pre-determined similarity degree, a sample trademark with a highest similarity degree to the image feature information about the trademark to be retrieved, and a corresponding figurative element code of a trademark; S 105 , acquiring and confirming a figurative element code of the trademark to be retrieved; S 106 , taking the figurative element code confirmed as a retrieval condition to carry out matching retrieval, and finding out a sample trademark matching the confirmed figurative element code; S 107 , collecting a retrieved result acquired by taking the image feature information about the trademark to be retrieved as the retrieval condition and a retrieved result acquired by taking the confirmed figurative element code as the retrieval condition; and S 108 , sequencing collected trademarks according to the similarity degree of the image feature information and reporting a trademark search result, wherein the extracting and processing image feature information about the trademarks in S 102 and S 103 includes: performing at least one of preprocessing procedures including graying, binarization and denoising, for a trademark; extracting a contour feature line from an image of the preprocessed trademark, wherein the contour feature line includes a set of edge pixels, a set of external contour line pixels and a set of inner contour line pixels of the image of the preprocessed trademark; positioning the direction and an extracted square or rectangle for the contour feature line in a coordinate system, wherein the coordinate system is constructed so that each pixel of the figure is defined by measurement units in an X axis and a Y axis; extracting a coordinate value G n (x n , y n ) of a pixel in the contour feature line in the coordinate system, wherein the subscript n represents a n-th pixel; representing the coordinate value G n (x n , y n ) with a relative number according to a preset rule, thereby acquiring a relative coordinate value S n (x n , y n ), wherein values of x n and y n in Sn are represented by relative numbers (percentages), and the x n and y n in Gn are represented by absolute numbers; rounding the relative coordinate value S n (x n , y n ) according to a preset distortion tolerance parameter and a rounding rule of “omitting decimal fractions smaller than 0.5 and counting all others, including 0.5, as 1”, to acquire a rounded relative coordinate value Z n (x n , y n ); establishing a subfigure segment of the image of the trademark; and extracting and processing image feature information of the subfigure segment, to acquire a relative coordinate value S n (x n , y n ) of the subfigure segment and round the relative coordinate value S n (x n , y n ).