The microstructure and mechanical properties of Al_0.1CoCrFeNi single crystal high entropy alloy (HEA) under axial tensile loading at room temperature (300 K) were investigated by molecular dynamics method. The tensile properties of the single crystal HEA were analyzed by changing the simulated strain rate and temperature. The microstructure and tensile properties of the single crystal HEA with small surface cracks were studied by simulating tensile experiments at room temperature. Results demonstrate that the tensile strength is increased with increasing the strain rate in a certain range; the Young's modulus and tensile strength are increased with decreasing the temperature at strain rate of 10¹⁰ s^-1. The single crystal HEA with small through cracks on surface presents a necking phenomenon after stretching for a period, and the stress concentration occurs at the crack tip along with the rapid development of a large number of slip dislocations, resulting in the rapid fracture.