Abstract: The phase shifter is a key part of high power phased antenna arrays whose beam of radiation can be steered. A high power rectangular waveguide phase shifter was designed. A metal piece is inserted into the waveguide paralleled with the narrow sidewall of the rectangular waveguide. The metal piece brings an agitation of the electromagnetic field in the waveguide. Moving the metal piece in the waveguide along the wide sidewall direction leads to continuous shifting of phase. 0-360 phase shifting can be obtained by optimization of the structure of waveguide and metal piece. Low insertion loss can be achieved by optimization of structure of metal piece. The phase shifter is completely metallic, so that it can hold high power microwave transmission. The operating frequency of the phase shifter is 9.4 GHz, and the length is 30 cm. The max shifting phase is 360, the max insertion loss is less than 0.2 dB, the power handling capabilities of the shifter is more than 64 MW. The measured insertion loss is less than 0.5 dB, and the measured phase versus frequency is linear.