Abstract: There are diverse conclusions in the study of the two aspects-critical force of buckle of drill string in horizontal well and the contact force of buckled pipe string on borehole wall. This paper analyzed the diverse theoretical and experimental conclusions and pointed out the reasons of occurrence of the diverse conclusions-the first is about different deduction methods and the second is unspecified test conditions. In order to reach correct conclusions, it is necessary to set up a scientific calculation method combining theoretical research, pilot tests and rig-site experiences.