Abstract: An instrument is designed to test the maximum bolting force in no-destructive inspecting through measuring the force and the displacement of the bolt and meantime drawing the F-S diagram timely.This instrument can distinguish the inflection point of the F-S diagram and give an alarm intelligently.Stopped at the maximum bolting force,it show us practically the same diagram in the second drawing.It is confirmed by field tests that this method can determine the max F of the bolted system accurately but not destroy the bolting structure,and the purpose to test the max F in no-destructive drawting become true.