The present invention relates to an automatic terminal fitting device for four-pin electrical connector which may comprise a rack, power control box and conveying device provided on the rack. A rubber shell vibration disc, a terminal fitting mechanism, and a back cover vibration disc are provided on the rack along the transporting direction. The rubber shell vibration disc is connected to the front end of the conveying device by a rubber shell transportation rail. The terminal fitting mechanism is provided on the back side of the conveying device and engages with the terminal feeding device provided on the rack. The back cover vibration disc is provided on the back side of the conveying device, to the right side of the terminal fitting mechanism. And the terminal fitting mechanism may include four sets of terminal fitting devices sequentially provided on the back side of the conveying device. On the right side of the terminal fitting devices, a terminal strip bending device engaging with the conveying device is provided. The present invention effectively addresses the problems existing when fitting terminals manually during assembly, such as low production efficiency, high manpower consumption, intensive labor investment, relatively high potential safety hazard occurrence, and unsatisfactory connector defect rate.