Abstract: Phase shifter plays a very critical role in the RF system of linear accelerators. To ensure the stable operation of high power accelerators, phase shifters which can withstand high RF power should be adopted. Based on the phase-shifting method of changing transmission length, a composite structure which can be adjusted by changing electrical length and tuned by 3 dB hybrid coupler was designed. After the optimization of each part with performance analysis and the simulation of the entire structure, a high power phase shifter was developed. The test results show that the operating frequency is 975 MHz, and the VSWR (voltage standing wave ratio) is 1.02 at this frequency. The output phase can be changed between 0° and 360° linearly, and in the whole phase shifting range the insertion loss is below 0.45 dB.