The invention discloses a method for detecting the shape of a mushroom, which comprises the following steps of: performing two-value segmentation, filtering and boundary detection on a side image of the mushroom to obtain the boundary of the mushroom; performing segment detection on N continuous boundary points on the boundary of the mushroom to obtain K segments; and performing segment overlap detection on 2N boundary points among segment pairs, recording the segment as a pileus lower edge segment if the related coefficient of fitting a straight line is greater than a segment overlap detection threshold value and the segment interval is greater than a stipe threshold value, performing clockwise rotation on a pileus by taking the inclination angle AHL of the pileus lower edge segment as an rotation angle to obtain a left boundary point, a right boundary point and a vertex of the pileus, and calculating the sum of a left chord height-length ratio and a right chord height-length ratio of the pileus to obtain a mushroom shape description factor. The boundary of the pileus is obtained by using the segment characteristic of the pileus of the mushroom and the mushroom shape description factor SM is obtained by calculating the left chord height-length ratio and the right chord height-length ratio of the pileus, so that the shape of fresh mushroom is automatically detected.