Abstract: The appearance of military stealth targets is a big challenge for radar detecting and tracking. Track-before-detect(TBD) algorithm is a very effective approach to solve the problem. An overview on track before detect algorithms is presented in this paper. Firstly, the basic principle of four TBD algorithms is introduced, which are three dimensional matched filtering(3DMF),Hough transform(HT), dynamic programming(DP) and particle filter(PF). Then the development on the study of the four TBD algorithms is reviewed. Finally, the trend of TBD algorithms predicted on the basis of analyzing the current TBD algorithms.