In the research project of high performance free electron laser, it is necessary to absorb the residual power at the end of its acceleration structure. At the operating frequency of 11.424 GHz, the RF load with the VSWR (voltage standing wave ratio) of less than 1.1 and high power absorption capacity needs to be developed. The software CST (Computer Simulation Technology) is used to design the loads. For the cylindrical water chamber water load, the design VSWRs are 1.0325 and 1.0533; At 50 MW peak power, the peak field intensities are 21.16 MV/m and 17.57 MV/m; the test VSWRs are 1.0582 and 1.0763. The effect of dielectric properties of ceramic and water on VSWR is also investigated. For the cylinder-shaped water load, the simulation results show that it has a high power tolerance level. For the dry load, the length of the load and the structure of the absorbing tooth are optimized to make it more convenient for machining. The results of thermal stress analysis calculated by ANSYS show that the maximum temperature and stress are 83.478 ℃ and 63.917 MPa respectively, and the maximum deformation is 0.072 971 mm.