Abstract: As a kind of space-based measurement system, because of the inaccuracy of datum mark and the influence of correlated factors, big LOS error exits in the measurement data. Firstly the error soures of the system are divided into two types: the early warning satellite orientation and infrared sensosrs revise. Then analyze the error reasons concretely, construct the submodel. Finally based on the child error model, construct the integrate system error model, and the model is verified by simulation.