A design of monitoring system for gaseous contamination indoors which used the technology of wireless sensor network based on ZigBee is put forward. The tree topology is used in the connection among the coordinators, the routers and the sensors. The SoC technology is also applied to the design of hardware about the nodes. The design of software application is presented on the above technologies. This system has many characteristics such as low complexity, small cubage, low energy consumption, simple operation, little harm to the mankind and so on.