Abstract: The HARQ scheme, in which chase combining algorithm is applied, is proposed based on TD-SCDMA system, and tracking merger HARQ algorithm is given. Two performance indicators, which are throughput and false piece rate, are used to measure the advantage and disadvantage of the algorithm. The downlink performance under some conditions such as different channel environment or different control parameters is simulated. Simulation results exhibit the effectiveness of the chase combining HARQ scheme in reducing block error rate (BLER) as well as in increasing throughput. Also, through the experiments it is found that the more retransmission time in chase combining, the smaller BLER in the downlink.