Abstract: Fatigue tests are performed on the plain concrete of two or three grades subjected to variable-amplitude biaxial tension-compression and triaxial tension-compression-compression cyclic loading by using a large multiaxial machine, and the residual strain of concrete is analyzed. The experimental results show that:under tension-compression and tension-compression-compression fatigue loads, the residual strain of concrete is mainly associated with the relative fatigue cycle and lateral compressive stress ratio, but has little relationship with the loading process. Furthermore, the relative residual strain is defined as the damage variant, and the damage evolution equations for plain concrete are established. On this basis, the damage analysis and prediction of fatigue remaining life are conducted, which provides a reference for variable-amplitude fatigue tests and fatigue damage evaluation of concrete under multiaxial loads.