Abstract: The electron gun, RF cavities and focusing magnet system were optimized and tested for the 45 MW experiment klystron. The design was proved to be feasible and reasonable. The test results show that this experimental klystron produces an output power of about 45 MW at 300 kV with an efficiency of 42%, repetition rate of 12.5 Hz, pulse width of 2 μs and gain of 49 dB. The perveance of the klystron is usually 2.05 μp, and the initial tests agree with the design prediction. From the relationship between output power and high voltage, the design and optimization of RF cavity and focusing magnet system meet the demands of the homemade 45 MW klystron.