For solving the problem that vehicle laser radar cannot measure range and speed simultaneously, we proposed a method of modulating amplitude of transmitting laser by pseudo-random noise code. At the receiving end, we measure target range by calculating correlation function of laser echoes and the local modulating codes, and target speed by analyzing spectrum of beat signal between laser echoes and local reference signal. Firstly, we show the schematic diagram, and discuss the inherent problem existing in the pseudo-random noise code modulated laser radar. Then, we proposed a novel spectrum analysis method for calculating beat signal. Finally, we verified the feasibility of the proposed method by numerical simulations. The results show that maximum speed that can be measured can be extended to 360 km/h without reducing the range measurement performance of current laser radar.