A ranging system using two-frequency laser was demonstrated, and the lidar-radar system concept was introduced. The two-frequency coherent laser beam carrying 100 MHz radio beat frequency was obtained by a monolithic nonplanar ring single-frequency oscillator and an acousto-optical modulator, and used as a probe. Through the optical transmitting and collecting system, the displacement of the object mounted on a motorized translation stage was detected. In the signal processing, the electronic heterodyne demodulation method was adopted to deal with the signals received by high-speed photodiodes. The displacement was obtained by calculating the phase difference between reference and detection signal achieved by a high-frequency lock-in amplifier. The ranging system turns optical heterodyne into electronic heterodyne demodulation, and the repetition error is less than 3%. The system takes advantage of the signal processing technologies of radar, and meanwhile, maintains the advantages of laser detection. The ranging system provides a good repetition.