The invention provides a vehicle door hinge mechanism, and belongs to the field of vehicles. The vehicle door hinge mechanism is used for connecting a vehicle door and a vehicle body of a vehicle, and comprises a vehicle body hinge seat fixedly connected to the vehicle body, a bent arm with one end rotationally connected to the vehicle body hinge seat, and a vehicle door hinge seat with one end detachably connected to one end away from the vehicle door hinge seat, of the bent arm, through a rotary pin, and with the other end fixedly connected to the vehicle door, wherein the connection and detachment of the vehicle door and the vehicle body are realized through the fixation and detachment of the vehicle door hinge seat and the bent arm, and the opening and closing of the vehicle door relative to the vehicle body are realized through the rotary connection of the bent arm and the vehicle door hinge seat. A detachable part of the vehicle door hinge mechanism provided by the invention is arranged between the vehicle door hinge seat and the bent arm, and the fixation and detachment are carried out through the rotary pin; and secondary debugging is not needed during re-assembly due to the high assembly accuracy of the rotary pin, so that the assembly efficiency is effectively increased.