The invention relates to a target detection method for an SAR (Synthetic Aperture Radar) image based on deep reinforcement learning, which comprises the steps of S1, setting the number of iterations,and sequentially processing images in a training set in each iteration process; S2, inputting an image from the training set, and generating training samples by using the Markov decision process; S3,randomly selecting a certain number of samples, training the Q-network by adopting a gradient descent method, obtaining the state of a reduced observation area, generating a next sample until a presettermination condition is met, and terminating the image processing process; S4, returning back to the step S2, continuing to input the next image from the training set until all images are completelyprocessed, and terminating the current iteration process; S5, continuing the next iteration process until the set number of iterations is met, and determining network parameters of the Q-network; andS6, performing target detection on an image in a test set through the trained Q-network, and outputting a detection result. The target detection method obtains good detection accuracy in target detection for the SAR image.