Li, X.X. JACoW Publishing Geneva, Switzerland Side coupled drift tube linac (SCDTL) was selected in the middle energy accelerator of the cancer treatment device, which works at 3 GHz. The periodic structure of six accelerator cavities has been completed, and it can accelerate proton from 10 to 20 MeV. Besides, the electromagnetic design and preliminary cold measurement of a single accelerator cavities (b= 0.15) have been finished. The frequency of single-cavity electromagnetic design is 2.961 GHz, the Q₀ value is 12498, Kp is 2.19. The initial measurement frequency is 2.9579 GHz, the Q₀ value is 6927, which is 55\% of the design value, but the Q₀ value can be improved by electrochemical polishing, so the experiment of increasing the value of Q₀ is being carried out.