The helium radiation damage of copper was simulated by using the molecular dynamics method, and the change process of copper microstructure under helium irradiation was observed on the atomic scale. The changes of the microstructure and mechanical properties of copper induced by helium radiation were analyzed, and the single crystal copper and the polycrystalline copper were compared. It is found that, the number of defect pairs in single crystal copper increases first and then decreases with the increasing number of helium atoms, and the peak value increases continuously. The number of defect pairs of polycrystalline copper continues to increase, but the fluctuation rule is not obvious. The tensile property test shows that the yield strength of copper is reduced because of the helium radiation. When the helium atom content reaches 0.54%, the yield strength of single crystal copper and polycrystalline copper is reduced by 46.94% and 49.2% respectively.