WiFi and ZigBee are regarded as key technologies of smart home, they support complementary applications in terms of data rate and serving range. Since both WiFi and ZigBee are operating over 2.4GHz Industrial, Scientific, Medical(ISM) band. And their devices are possibly close to each other for huge number of sensors or controllers in smart home scenario. The coexistence between WiFi and ZigBee system under smart home scenario is a critical issue. In this paper, an overview of WiFi-ZigBee interference analysis methodology, modeling of CSMA/CA mechanism and detailed coexistence issues under smart home scenario are introduced. Afterwards, two representative network deployment cases are simulated and discussed from their Clear Channel Assessment (CCA) mode and device distribution density. Results indicate that ZigBee system can work normally under the interference of WiFi deployed in the adjacent frequency band, if proper CCA mode is applied.