The invention discloses a fatigue testing machine applied to a tension test piece. The fatigue testing machine is mainly used for a tensile test and a tensile fatigue test for mechanical components. The testing machine comprises a fatigue force application mechanism, a pretightening force mechanism, a straightening roller mechanism, a test fixing frame, an auxiliary mechanism and a control system. A power system of the fatigue testing machine comprises the fatigue force application mechanism and the pretightening force mechanism; the tensile force output by the power system is redirected by the straightening roller mechanism and is transmitted to the tension test piece; and the fatigue force application mechanism, the pretightening force mechanism, the straightening roller mechanism and the auxiliary mechanism of the fatigue testing machine are arranged on the test fixing frame. The fatigue testing machine has the advantages of adopting hybrid pneumatic and electric power as the power system of the fatigue testing machine, mastering numerous parameters including the maximum average displacement, the minimum average displacement, peak displacement, the maximum average tension, minimum average tension, minimum fatigue tension, frequency, accumulated test times, accumulated test time and the like, and providing a basis for optimization design of the tension test piece.