A compact cavity filter with capacityloaded structure is designed in this paper. A disc shape end of the resonator is adopted to realize capacityloading, and Teflon support structure is used to reinforce the resonant post. In the calculation process, the lumped ports are added into the 3D electromagnetism model, and then the cosimulation with circuit model can optimize parameters more efficient. The power capacity analysis is carried out under 3D electromagnetic environment, and the results show that the filter meets the requirements of high power index.