Abstract: A novel track-before-detfect (TBD) algorithm based on Modified Hough Transform (MHT) and Particle Filter (PF) is proposed to solve the shortcomings that the real target trajectories cannot be obtained for many false trajectories existing in the TBD algorithm based on Hough Transform. Firstly, possible trajectories are initiated by the MHT to obtain the region of location of the target, then this region as the prior knowledge is provided to the PF and the likelihood function is established for target detection by the weights which are calculated by the PF, at last the false trajectories are eliminated and the real target trajectories are given with detection results. Simulation results show the presented algorithm can implement accurate tracking and detection weak target.