The development of a high-gradient accelerating structure is underway to construct a compact proton linear accelerator for cancer treatment.Extensive experiments and numerous studies are being conducted to develop compact linear accelerators for proton therapy.Optimiza-tion of the electromagnetic and mechanical design has been performed to simplify the manufacturing process and reduce costs.A novel high-gradient structure with a low relativistic proton velocity(β),v/c = 0.38,was designed,fabricated,and tested at high power.The first full-scale prototype was also successfully tested with high radio frequency(RF)power,a repetition rate of 50 Hz,and pulse length of 3 μs to reach a high-gradient of 46 MV/m using a 50 MW S-band klystron power supply obtained from the Shanghai Soft X-ray Free Electron Laser Facility.This is the first high-power test in China,which is in line with the expected experimental goal.This study presents prelimi-nary high-power testing of S-band standing wave acceler-ating structures with 11 cells.This work aims to verify the feasibility of using a high-gradient RF accelerating struc-ture in compact proton therapy facilities.The cold test of the prototype cavity was completed in advance.Details of the high-power RF test setup,the process of RF condi-tioning,and the high-power results are described.