A good bonding between the high-entropy alloy (HEA )CoCrFeMnNi and pure Cu is obtained at 750-850 ℃ by vacuum solid-state diffusion welding. The influence of bonding temperature on the interfacial behavior and the joints mechanical properties is investigated by scanning electron microscopy,energy disperse spectroscopy,microhardness test and tensile test. The diffusion coefficient of Cu in CoCrFeMnNi HEA is calculated and analyzed by fick’s second law. The results show that the diffusion rate of Cu in HEA side is faster than that of HEA elements in Cu side and, as increasing with the temperature ,the reduce extent of the HEA elements concentration distribution in the diffusion area agree with the sequence of elements in the order of Mn>Cr>Fe>Co>Ni. Theoretical calculations show that the average diffusion coefficient of Cu in HEA is significantly lower than those in the reference stainless steel. After diffusion bonding,a reaction layer consisted with FCC solid solution is formed in the interface region of all the joints,and there is no intermetallic compounds appeared. All the joints fracture occurred only in Cu sides far away from the interface,the tensile strength and strain all decrease as the bonding temperature increase. In the bonding temperature of 750 ℃,the tensile strength and strain reach its maximum value of 224 MPa and 33%,respectively.