The mechanical behavior and microstructure evolution of Mn18Cr18N steel under cycle loading in the strain amplitude range of ±0.005-±0.10 were studied by room temperature tension-compression cycle loading tests. The microstructure evolution of Mn18Cr18N steel, including metallographic structure, dislocation morphology, deformation twins and other substructures, were observed by optical microscope and transimision electron microscope. The research results show that the cyclic mechanical properties of Mn18Cr18N steel are related to the strain amplitudes in the tension-compression cycle loading. With the increasing of cyclic strain amplitude, the cyclic stress amplitude of Mn18Cr18N steel shows an increasing trend. When the strain amplitude is ±0.10, the rheological stress of Mn18Cr18N steel is 988.1 MPa after one cycle loading, which is 1.6 times of the 0.2% initial yield strength. The research  indicates that the cumulative plastic strain of Mn18Cr18N steel is increased by the cycle loading with large strain amplitude to significantly improve the strength. At a lower strain amplitude (±0.005-±0.01), the deformation of Mn18Cr18N steel is mainly plane slip, and the dislocation rearrangement and the activation of other slip systems are the main reasons for the cycle softening of Mn18Cr18N steel. When the strain amplitude is larger, the proliferation of high dislocation increases the internal stress of the matrix, the local area slips difficultly, the twinning mechanism is activated, and Mn18Cr18N steel generally exhibits cycle strengthening characteristics.