The invention discloses a pressurization and oil supplement device outside a power capacitor tank. The pressurization and oil supplement device comprises a base, wherein a fixed block is arranged at an upper end of the base, a groove is formed in an upper end of the fixed block, a device cavity is formed in an inner wall opposite to the groove, multiple groups of arc blocks are arranged on an inner wall opposite to the device cavity and are opposite in positions, limitation grooves are formed in side walls of the arc blocks, a push rod is arranged on a side wall of the fixed block in a penetrating way, a limitation block is arranged on the push rod and is matched with the limitation grooves, a handle is arranged at one end of the push rod, a prop block is rotatably connected with one end,far away from the handle, of the push rod and is fixedly connected with an inner wall of the groove via a buffer device, a round cavity is formed in an internal bottom part of the groove, and a movable rod is arranged in the round cavity and is fixedly connected to an internal bottom part of the round cavity via a spring. The pressurization and oil supplement device is reasonable in structural design and simple to operate, the clamping of a capacitor is facilitated, oil injection is convenient, and the oil injection efficiency of the capacitor is greatly improved.