Based on the characteristic analysis of images under deep space background, a new method for dim target detection under deep space background was proposed based on topological invariance.Firstly, the image matching method based on topology invariance was adopted to match the sequential images with the first-frame image as baseline.Then, the background of the sequential images was removed.Finally, the method of Hough transform was used to detect the dim target in the image, so as to obtain target information.In order to verify the effectiveness of the proposed method, a series of semi-simulating sequential images were made by using the STK software, and an experiment was carried out.The results showed that:1) The detection ability of the proposed algorithm exceeds that of SMP and SBV;and 2) The computational efficiency of the proposed algorithm is equal to that of the SMP algorithm, and is higher than that of the SBV algorithm.