The invention discloses a complex load rotary fatigue tester mainly comprising an experiment kettle body being a cylindrical tank body. A circulating system is arranged in the experimental kettle bodyand includes a circulating loop; and a pump is arranged in the circulating loop and is connected with a corrosion gas pipeline. A clamping device is arranged in the experiment kettle body and used for fixing a test piece. An extension bar is installed at one side of the experiment kettle body and is used for applying a shear force to the test piece. The lower part of the clamping device and the extension bar are respectively connected with a power system. According to the invention, an axial alternating load and a tangential alternating load can be applied to the rotary test piece at the sametime to simulate the stress condition of the test piece under the action of a complex load. Since solid-phase particles with a certain concentration are also added into the kettle body except corrosive gas and liquid, an erosion environment can be simulated.