The present invention discloses a point cloud mean background subtraction based method for 3D sonar image modeling, comprising: (1) obtaining sonar data, and convert 3D sonar range image information corresponding to sonar data per frame into point cloud data for overall coordinate; such point cloud data will form image pixels; (2) taking the mean value u(x,y,z) of pixels at the same position in a series sequential frame images as pixels at the same position in the background model to obtain the background model; define threshold value TH for background standard based on pixel in each image; (3) testing current frame image I(x,y,z) based on background model and threshold value TH to obtain output image; (4) using current frame image I(x,y,z) to update background model and threshold value TH. Such method can quickly identify prospect target in the background, and establish corresponding arithmetic model for further processing; it features in quick processing, which can automatically update background model according to changing environment.