Abstract: In common medical/industrial linac systems, ordinary magnetron as the power source has been adopted for about 20 years. Despite of the low power level and the short life time, magnetron is the only choice to drive the compact linac system due to its size and weight. With the development of multi-beam klystron technique, working voltage and the system size can be reduced dramatically while the power level and average power have taken a big step forward. Typically, a magnetron in X-band can supply a 2 MW microwave power maximum, which gives great challenge for the linac system engineering. To meet the demands from medical and industrial applications, high-power klystrons were developed for cancer treatment, nondestructive inspection and industrial irradiation. This paper introduces an X-band high-power multi-beam klystron with 3 MW output power at 9300 MHz. Compared with the magnetron power source, the linac cavity could be reduced by 30%. Based on the integrated coil and oil cooling system, the boundary dimension could be reduced to ϕ200 mm×400 mm with the total weight of 25 kg.