Abstract: In adaptive optics the wavefront sensor is one of the key components . It must be able to detect the wavefront distortion caused by air turbulence within the photon noise limitation and in a few milliseconds of time. Because of that, the stars or space objects under observation usually are very feint and the time frequency of air turbulence is as high as 1000 Hz . An experimental study on the Hartmann type wavefront sensor based on photon counting technique has been carried out. The experimental results show that a wavefront distortion detection sensitivity of A/10 has been reached for space objects with 8th astronomical magnitude within 1 ms. An algorithm and computer program related to the luminous flux and to the photoelectron rates for wavefront sensors have also been established and verified by experiments .