The invention provides a waveguide circulator comprising a waveguide cavity, two gyromagnetic ferrites, a plurality of permanent magnets and two adjusting devices. Each adjusting device is provided with a first through hole and a second through hole. The magnitude of a magnetic field of the gyromagnetic ferrites is changed by changing the placement position of the permanent magnets in the adjusting devices. The invention also provides a commissioning method. The method includes determining the number of the corresponding permanent magnets required according to the magnitude of the magnetic field required for the gyromagnetic ferrites; first placing a permanent magnet in the first through hole of each adjusting device for commissioning; if the preset range cannot be satisfied, moving the permanent magnet into the second through hole, rotating the adjusting devices for a plurality of times to drive the permanent magnet to rotate around the axis of the adjusting device until the reading of a vector network analyzer meets the preset range and completing the commissioning. Compared with the conventional method of eliminating the error by increasing or decreasing adjusting pieces in an upper cavity and a lower cavity, the commissioning method reduces the operation complexity and improves the commissioning efficiency and success rate.