[en] Especially for the applications of X-ray lasers, X-ray multi-layer reflector is an important element for soft X-ray optics. With developing of the X-ray lasers and its applications, the uses of the X-ray multi-layer reflector become more wide-ranging. But the plasma environment which creates X-ray laser brings the difficulties to the application of X-ray multi-layer reflector. The biggest difficulty is that the X-ray emitted by the plasma destroys and damages the multi-layer reflector. It is shown by the experiments that the damage threshold of Mo/Si multi-layer reflector made in China is less than 0.10 J/cm². Under the exposure to this radiation dose, the root-mean square roughness of multi-layer apparently increases and the reflectivity almost drops to zero. According to these results, the authors give some ideas for preventing damages of the multi-layer reflector