The invention relates to a pre-tightening type mechanical clamping mechanism for combined load material mechanical property testing, and belongs to the technical field of material testing. The self-locking property of a wedge block is utilized, and the pre-tightening mode of the wedge block is adopted, so that a test piece is reliably clamped, and meanwhile the clamping requirement for various loading modes such as stretching, bending and torsion during independent or combined usage can be met. Silicon nitride heating pieces make contact with the two sides of the clamping end of the test piece for heat conduction heating to change the test temperature. Electric field loading is performed by guiding controllable current into the test piece. The magnetic field environment is applied to the test piece through a controllable electromagnet. Combined loading of a physical field and mechanical loads, and a material testing test is performed on the closer service condition. The structure is simple and compact, operation is convenient, the larger initial clamping force and higher clamping stability can be provided at the same time, original compressing force brought by pre-tightening force is eliminated before the testing, the testing result is more accurate, and the high application value is achieved.