The invention provides a reliability test bench with a torque loading function for a gantry boring and milling machine accessory milling head. Two groups of supporting and driving components are respectively used for fixing and driving a right-angled type accessory milling head and an elongation type accessory milling head; the two output ends of a transmission in a torque loading component are respectively connected with the two accessory milling heads; each of the two accessory milling heads adopts a drive motor and a power source, is connected with the drive motor through a belt transmission pair and is fixedly mounted on the inner side of a corresponding accessory milling head supporting component; the two accessory milling heads and an output shaft of a gearbox are respectively connected by adopting an elastic shaft coupling; an automatic control component is used for acquiring torques and rotating speed signals at the two output ends of the transmission and controlling the running states of the drive motor and a dynamometer. The reliability test bench provided by the invention realizes reliability test performed on the gantry boring and milling machine accessory milling head under the condition of simulating actual conditions and overcomes the defect that a reliability test device for an existing gantry boring and milling machine accessory milling head cannot simulate the load torques and can only perform a running-in test.