The invention relates to the technical field of electric engineering, in particular to an automatic voltage adjusting transformer. The front sides of adjusting cores are connected with springs. The other sides of the springs are connected with permanent magnets. The rear portions of the permanent magnets are connected with movable rods. Each primary coil is provided with a groove. The movable rods are connected with the grooves. The length of the movable rods can be adjusted according to situations, the maximum number of the shielded primary coils can be precisely controlled, the output voltage of the transformer can be reasonably adjusted, and the output voltage of the transformer is stable.