Abstract: A measuring method of aerial camera lens- focus plane is presented, which locates focus plane using autocollimation theory. The system chooses two kinds of image definition evaluation function to extract the characteristics of image definition, and detects focus plane quickly using hill-climbing algorithm. Simulation experiment result proves that measuring and calibrating the focus plane of aerial camera using the autocollimation measuring system is characterized by high precision, high speed and good real-time performance, and has little influence by the artificial factors. The system is adapted for the focus plane calibration and auto-focusing system of aerial CCD camera.