High speed pseudorandom modulation and photon counting techniques are applied to a three-dimensional imaging lidar system. The specific structure and working principle of the lidar system is described. The actual detector efficiency of a single-photon detector in an imaging system is discussed, and the result shows that a variety of reasons lead to the decrease in detection efficiency. A series of ranging and imaging experiments are conducted, and a series of high-resolution three-dimensional images and a distance value of 1200 m of noncooperative targets are acquired.