Aiming at the problems of noises and pseudo-edges in the extraction of radar image edge, two improvements are made to the traditional mathematical morphology edge detection algorithm: first, the radar image is filtered by using nonlinear composite mathematical morphology filtering method; second, according to the characters that different elements extracted result different operations, to construct a new mathematical morphology edge detection algorithm by using the idea of multi-structure elements. The experimental results show that the two algorithms solve the contradiction between signal-to-noise ratio and single-edge response to a certain extent, and realize the three indexes of Canny’s edge detection performance, and keep more characteristic edge information in radar image.