To date, few researches describe the evaporation for Al well in superalloy during electron beam (EB) melting, for the reason that Al has a very high saturated vapor pressure but has a relatively low evaporation. In order to study the evaporation for Al, EB technology has been used to remelt a multi-component Ni-based superalloy K417 in our work. The difference between melting and smelting procedure has been emphasized particularly. The weighted average mixing heat was used to describe activity coefficient, and the effective temperature during 9, 12 and 15 kW EB smelting is 2290, 2320 and 2430 K, respectively. In addition, Al evaporation was described well after compensation and the corresponding compensation constant ω is suggested to be applicable for Ni-based superalloy preparation. This work shows its significance in theoretical guidance for the preparation of Ni-based superalloys.