Intensified change coupled device (ICCD) is one of the key devices in the staring three-dimensinal (3D) active imaging laser radar. The intensity and noises were measured with different input light intensities and different intensified gain voltages. According to the photoelectric detection process, the measured intensity and noises are analyzed with Poisson random process theory and the least square fitting method. It is found out that the noises consist of the equivalent photoelectron shot noise from the image intensifier and the photoelectron shot noise from the charge coupled device (CCD). Although the optical signal is magnified by the image intensifier, the latter part of noise can not be neglected in most cases. A noise model of 3D imaging with a doubly stochastic Poisson process is established, from which the optimal range-modulated gain function with a minimum distance error is deduced.