By simultaneous switching of transmitting and receiving beams in an electro-optical device, a novel laser ranging method is proposed. Continuous wave (CW) laser emitted by laser transmitter goes forward to the measured object, being reflected by the object, then goes back to the transmitter. Close to the transmitter, an electro-optical crystal is added into the round-trip light rays. High voltage curve with the steep enough edges is added on the crystal. Because of the high speed switch effect, the crystal operates on the transmitting and receiving beams at the same time. So light pulses, whose width T contains the required range information, are cut off and detected. In experiments the changing time of high voltage is about several nanoseconds realized by avalanche triode circuit. And based on double refraction and total internal double reflection effect in crystal, a single block LiNbO3 crystal with special shape is designed as the main device of this method. The feasibility of the new idea is proved by the results from oscillograph. So a brand-new way for the laser ranging is provided.