The effect of different solution treatments on the microstructure and element segregation of AM3 nickel-based single crystal superalloys with the carbon content of 0.045wt% was investigated. The optical microscope (OM) and scanning electron microscope (SEM) were used to observe the microstructure and γ' phase of AM3 superalloys, and the electron-probe microanalysis (EPMA) was used to analyze the element segregation. The results show that the incipient melting temperature of the AM3 superalloys is 1305 °C. After the solution treatment of 1305 °C/6 h following the homogenization treatment of 1300 °C/3 h, the incipient melting structure is reduced, and the incipient melting temperature is increased by about 5 °C. With increasing the solution temperature and prolonging the solution duration, the volume fraction and size of the precipitated γ' phase are increased significantly, and the segregation ratio of Cr, Co, Mo, W, and Al elements is closer to 1. The existence of incipient melting structure prevents the segregation of Ti in AM3 superalloys with prolonging the solution duration after heat treatment. Thus, the optimum heat treatment process is 1300 °C/3 h+1305 °C/6 h/air cooling (AC)+1080 °C/6 h+870 °C/20 h/AC. The dendrite structure of AM3 single crystal superalloys completely disappear after heat treatment. The cubic degree of γ' phase is improved, the size of γ' phase reaches 454 nm, the volume fraction of γ' phase is 66.05vol%, and the segregation of Cr, Co, Mo, W, Al, and Ti elements is significantly reduced.