The invention provides a flange tensile-flexural-torsional composite loading multi-bolt loosening testing machine, which can simultaneously apply tensile-bending-torsional composite load to a multi-bolt connected flange to study the bolt loosening characteristics. The testing machine belongs to the technical field of mechanical testing equipment. Transverse load generated by a three-phase asynchronous motor is taken as bending load applied to the flange, tensile force generated by a hydraulic puller is taken as axial tensile load, and torque generated by a servo motor is taken as torque load applied to the flange. Different from a conventional apparatus that applies two types of composite load to a single bolt, the testing machine can apply three types of composite load to the multi-bolt connected flange. The three types of composite load can be isolated from each other and do not interfere with each other, and load applied can be displayed in real time.