The principle of the interference between TD-SCDMA uplink and WCDMA downlink was analyzed, and then build system simulation model based on Monte Carlo. Adaptive variable step power control algorithm was used into the simulation. By simulation, traditional fixed step algorithm was compared with adaptive variable step power control algorithm, the coexistence interference of TD-SCDMA uplink and WCDMA downlink was simulated for speech users only in a macro-to-macro cells scenario considering 1920MHz frequency. The result shows that a higher SINR value is achieved by adaptive variable step power control algorithm if the total transmission power is invariant, so it could reduce the system interference. According to the simulation results, different parameters settings are presented about the coexistence influence between TD-SCDMA and WCDMA system, and ACIR value are provided about system coexistence. It provides valuable reference for the research of hybrid network planning and optimizing.