Abstract: The fatigue damage of non-magnetic materials of petroleum measurement while drilling（MWD） instruments increases the failure risk significantly. Its fatigue life and service safety evaluation were important references for the selection of drilling operation parameters. The mechanical properties of non-magnetic austenitic stainless steel P550 with MWD instrument were tested. According to high stress load characteristics of drilling operation, the high cycle fatigue tests of adjacent yield strength were carried out respectively. For the characteristics of fatigue life dispersion, a method to evaluate the fatigue life of P550 steel under high stress was proposed. The results show that the fatigue life of P550 steel is well matched with basquin model. The dispersion of fatigue life increases obviously with the decrease of stress amplitude. Moreover, the test life under low stress is lower than the predicted life, and the fatigue fracture mechanism changes with the decrease of stress amplitude. The crack propagation mechanism is mainly periodic cleavage when the stress amplitude is close to the yield strength, and ductile fracture at lower stress amplitude.