Maximum range is one of the major parameters of laser rangefinder and a basic guideline in system design.It will change with the detected goal.The detecting equation of lidar to particle-target was educed in this paper,and it could be used easily in practice.Laser′s far-field distributing affect maximum range.According to the practical detecting equation,the maximum range of a laser rangfinder was estimated,and it changed among 15.05~20.6 km with laser′s far-field distributing.The result was analyzed and discussed.It was found that if laser′s far-field distributing is flat and other parameters of the laser rangefinder is not changed,the system′s maximum range can be improved to 18.9 km.