A model for estimating the detection distance of an infrared imaging system with a focal plane array is established. Taking the influences of system observation environment conditions, infrared radiation characteristics of targets and infrared imaging systems with focal plane arrays on the detection distance into account, the model can estimate the detection distance of an imaging system for a specific flight target effectively. With this model, the key technical parameters of an infrared imaging system can be calculated and verified scientifically. Thus, the top design of a system can be strengthened, the theoretical foundation can be laid for the engineering practice and the development process of the relative imaging system can be instructed. Therefore, the model is of very important value to engineering applications.