In order to improve the stability and accuracy of the phase laser rangefinder for non-cooperative target,an improving transmitting and receiving circuits are designed.Its principle includes dual-frequency modulation,direct digital synthesizers(DDS),phase-shift technology and so on.Theoretical research,analysis and experiments are carried out.Sine wave generated by DDS is modulated and transmitted.The laser signal reflected from non-cooperative target is received.Modulator and transmitter circuits of the system are optimized.New electro-optic detector and high-voltage bias circuit are used.The experimental result shows that the ranging system is simple and effective,and has high accuracy and stability.