For the self-piercing riveting of high-strength steel and cast aluminum, combining experiment and numerical analysis, the key factors and mechanisms affecting the joint forming were studied. The results show that it is difficult to penetrate the lower plate when the rivet is too short, but using the excessively long rivet can easily cause the rivet legs to collapse. In the actual using, the length of rivet should exceed the total thickness of plate by 0.5-1.5 mm. Moderately increasing the rivet hardness can delay and shorten the time for rivet leg upsetting to improve the condition of rivet upsetting effectively. However, when the hardness of rivets is too high, it reduces the interlock value, which is not conducive to form a good joint. Increasing the strength and thickness of upper plate expands the range of force on the rivet feet, resulting in the rivet legs to expand outward. However, when the equivalent stress of rivet legs exceeds the tensile strength of rivet, it exacerbates the upsetting of rivet legs and affects the forming of joint. The ductility of cast aluminum lower plate is relatively insufficient, which is prone to joint cracking, and the cracking often occurs at the bottom edge of the joint protrusion with positive stress triaxiality. With the increasing of riveting die depth, the strain value of the protrusion bottom edge also increases, making it more prone to cracking. Therefore, the riveting die depth should be controlled within 0.9-1.0 mm.