The sensitivity of laser distance measuring instrument is studied ,and an easy-operation distance ability detection method is introduced. This method is designed based on the range equation and light extinction principle. Using the preknown objects and meteorological condition , changing the optical receiving area ,and making the detection power equal to the minim detection power , the minimum receiving area is derived. Using this receiving area , an given object is detected , and the distance ranging ability is regarded as meeting the challenge if the detection arability is larger than 95 %. This method is used in practice ,and the results are verified by the long distance objects , which shows that this method is good and practical.