The poisonous gas from chemical plant fire will harm surrounding residents. Therefore, to build the evacuation mechanism and operation procedures are very important. In this study, the ALOHA software was used to simulate the poisonous gas diffusion from chemical plant fire for different wind situations which located in Pingtung City. The results show the poisonous gas diffuse different direction and region depending on the wind direction. According to the results can build the residents evacuation mechanism and operation procedure and to reduce the residents dangerous when disaster occurred.