Doppler Blind Zone (DBZ) in pulse Doppler (PD) radar can cause the termination of target tracking and a repeated count of tracks. Aiming at solving this problem, an algorithm based on radar and IR data fusion was proposed. Before entering DBZ, the trajectory information of the target can be obtained by the joint tracking of radar and IR. When the target enters DBZ, it can be tracked continuously using the bearing information of IR and the trajectory information which was obtained previously. Simulation results show that the algorithm is feasible and it can be used to solve the tracking problem in DBZ.