Since the permission of WiMAX (802.16e) as a member in IMT-2000 enables it to use 3G systemspsila bandwidth by WRC-07, more researchers have paid attention on the analysis of coexistence issue between WiMAX and WCDMA systems in 2500 to 2690 MHz band. In this paper, the detailed interference environment analysis, including several interference scenarios, network deployment, propagation models and interference models, is described. Based on appropriate assumptions, some representative interference scenarios in which WiMAX and WCDMA systems are operated on the adjacent frequency bands are simulated and discussed from four different respects: separation distances for these two systems, base station antenna coupling loss, uplink power control mechanisms of WiMAX system and frequency reuse schemes. It is shown that the interference from MSs of one system to BSs of another system is not quite severe after using appropriate techniques. Meanwhile, a few suggestions are introduced to better deploy these two systems.