The principle of passive range measurement based on IRST system is presented.Aiming at the limitation of double-station IRST system,a passive range measurement with triple-station IRST system is introduced.Combining with actual application,the algorithm measurement precision is analyzed,and the error formula is given.The simulation results show that the passive range measurement with triple-station IRST system has good practicality,which could complete fine ranging from 0° to 360°.