A new rate model based on Generalized Laplacian Distribution is introduced in this paper. Compared to the traditional Laplacian Distribution,the model can better describe the kurtosis and tail distribution of DCT of video sequences.Besides,according to the new rate model,a lowdelay rate control algorithm adopting target bit allocation and Quantization Parameter (Qp) on Macroblock (MB) level is proposed.The compute complexity,which is caused by Qp obtained from MB variance in TMN8,can be reduced in the algorithm by adopting the method that the basic Qp is determined in frame lever and adjusted in MB level.Simulation results show that the proposed algorithm can effectively regulate buffer occupancy and reduce system delay.