Maximum range is one of the major parameters of pulse laser range finder, Several common measurement methods are analyzed. A novel method combining outdoor light extinction ratio with indoor time sequence gain coefficient ratio is proposed, For two pulse laser range finders, outdoor light extinction ratio, indoor time sequence coefficient and maximum range are measured and compared. The results and error analysis are given. The results prove that the maximum range of the pulse laser range finder whose operating wavelength is 1.06μm and 1.54μm could be measured accurately, and it is hardly effected by weather condition and target properties, nor is effected by time sequence gain circuit. The method has high accuracy, repeatability and serviceability . By this method, other major parameters of the pulse laser range finder such as ranging accuracy, gating range, gating accuracy and range resolution can also be measured.