The invention relates to a hydraulic circuit for locking an upper anvil block of a hydraulic forging machine and an oil supplying method. The hydraulic circuit is arranged on a component of the hydraulic forging machine. Control hydraulic oil of the hydraulic circuit directly comes from a hydraulic cylinder oil inlet cavity arranged in the hydraulic forging machine and fixedly connected with a movable beam. Hydraulic oil in the hydraulic cylinder oil inlet cavity controls work of a locking hydraulic cylinder. The locking hydraulic cylinder controls fixed connection or disconnection between the upper anvil block and the movable beam. Movably connected hydraulic hoses and pipeline drag chains as well as an independent oil supply pipeline from a hydraulic system and a control valve to the machine frame are omitted between the movable beam and a machine frame of the hydraulic forging machine, namely synchronous movement between the locking device oil supply circuit and the movable beam is achieved, the hydraulic locking oil supply circuit is simplified, and reliability is improved.