Abstract: Proton beam therapy (PBT) can achieve the effect of precision radiotherapy due to its unique Bragg peak. In the process of proton therapy, the peak can be accurately located to the tumor area, which can give the tumor a larger dose of irradiation, reduce the damage to normal tissues and organs, and reduce the occurrence of side effects. Therefore, it is very important to locate the Bragg peak of proton beam in real time in proton therapy. In this paper, a cyclotron is used to generate proton beam, and a diamond detector is used to test the radiation characteristics of proton beam, and the Bragg peak and the beam spot center are measured (0, 35 mm). Thus, accurate Bragg peak value of proton beam was obtained, which guaranteed the accuracy of proton therapy.