The invention relates to a division method for an extracted watershed SAR image with a threshold method and marking, which combines an OTSU threshold method and watershed marking, and uses an image after threshold division as a source for marking a watershed mark, thereby effectively eliminating the influence of grain information and obtaining a new division method for the watershed SAR image based on threshold division. The method comprises the following steps: (1) Gaussian low-pass filtering is carried out for an original image Img to obtain an image GImg after filtering; (2) gradient is calucated for the image GImg after filtering to obtain an gradient image PGImg; (3) internal marker LImg of the original image Img is extracted with an Otsu method; (4) a classical watershed conversion is carried out for the internal marker to obtain an external maker WLImg; (5) the gradient image PGImg is modified with the internal marker and the external marker, and the forcement minimum techniqueis utilized for the modification so as to enable a local least area to only appear at a marking position; and (6) watershed conversion is carried out for the modified gradient image to obtain a finaldivision image RImg. When the method is used for SAR image division, not only over-division can be reduced, but also the accuracy of the edge can be ensured.