In order to improve the measuring rate and resolution of a phase-shift laser range finder, a new phase shift magnification detecting method is proposed, which improves the measurement resolution by 1/N times without increasing the measuring time. Then, a under-sampling technique is adopted to perform multi-frequency modulation in the same system,which avoids using the mixer and other accessorial components to reduce scheme complexities and the influence of crosstalk. As the phase delay caused by the high frequency weak light incident upon a Avalanche Diode(APD) will induce the distance measurement errors, a new method is presented by controlling the bias voltage acting on APD to suppress the phase delay. For a modulation frequency of 18.5 MHz, a wavelength of 650 nm and an incident light intensity of 0.5 μW, the phase delay can be reduced from 1.4° to less than 0.03°. Moreover,a mathematic model is established based on the phase shift measurement errors caused by signal acrosstalks and several kinds of electrostatic screen methods are given to avoid the acrossatlk.Experimental results show that adopting those methods mentioned above can get the phase shift measurement resolution of 0.014° and the distance measurement resolution of 0.3 mm accordingly when the modulation is 18.5 MHz.