Due to the Doppler Blind Zone (DBZ), the target tracking of Doppler radar becomes more and more complicated. In this paper, a multi-target tracking algorithm based on Gaussian Mixture Probability Hypothesis Density (GM-PHD) for DBZ is proposed. The algorithm introduces the Minimum Detectable Velocity (MDV) information to the traditional detection probability model to update the GM-PHD and the updated equation of the GM-PHD is deduced. The simulation results show that, compared to the traditional GM-PHD with the only Doppler measurement, the proposed algorithm improves greatly the radar tracking performance of moving target under the condition of minor MDV.