Based on the fundamental principle oriented from the single beam klystron, multi-beam klystron can make higher peak output power under a lower working voltage with the help of parallel working mode combining several low perveance electron beams. Lower working voltage also makes a contribution to the compact design of the whole system. In the linac system design, input power source is the key factor that determines the composition of the whole system. The increasement of the source power can shorten the linac tube dramatically, thus make the brand-new application scenarios possible such as the high-degree freedom cancer treatment or the compact nondestructive testing system. The C-band multi-beam klystron in this article mainly targets on the low and medium energy accelerator applications, which can give out the microwave power at higher rep-rate (500 Hz) and higher working ratio (0.2%).