The invention relates to a small target detection method based on an improved Fast RCNN, which is realized by executing an improved Fast RCNN algorithm instruction by a processor, and comprises the following steps: receiving a scene picture containing a small target and extracting a first feature map F; obtaining a predicted anchor point frame a (x, y, w, h) according to the first feature map F1; obtaining a second feature map F2 with the same size as the first feature map F1 according to the first feature map F1 and the predicted anchor frame a (x, y, w, h); and obtaining a detection result of the scene picture according to the second feature map F2 and the predicted anchor frame a (x, y, w, h). According to the invention, modification is carried out based on a Fast RCNN algorithm framework, and the RPN network under the Faster RCNN algorithm framework is replaced with the adaptive anchor frame network, so that the generated anchor frame can be better matched with targets with different scales, thereby avoiding missing detection caused by unreasonable size of the anchor frame, and improving the detection accuracy.