The invention discloses an automatic nut mounting machine comprising a motor (1). The motor (1) drives a spindle (25) through a decelerating mechanism to rotate. A part conveying structure for conveying a workpiece (23), a nut conveying mechanism for conveying nuts (20) and a nut mounting mechanism for mounting the nuts (20) are connected to the spindle (25). According to the automatic nut mounting machine, a power system is driven by the motor, and decelerating is achieved through belt transmission and second-stage gear transmission; the structure is simple, and the cost is relatively low; and in addition, the function that the workpieces and the nuts are continuously conveyed can be achieved, the function of automatically mounting the nuts can be further achieved, and the multiple functions are integrated.