An optimal synthesis method of adjustable spherical four-bar mechanisms for multi-function generation was put forward. Different functions can be generated by the same mechanism through adjusting the length of the connecting frame poles. Based on the function relation between the input angle and the output angle of the spherical four-bar mechanism, the optimization model was established. The objective function was given with the aim of minimizing the maximum of the absolute structural error, and the constraints were given to ensure the crack existed and that the mechanisms have good transmission quality. After this, the immune genetic algorithm was chosen for multi-function generation of adjustable spherical four-bar mechanisms. The result of the synthesis example verified the effectiveness of the proposed method.