Compared with the conventional klystron, high power multi-beam klystron makes use of many low perveance beams, then it has a high output efficiency and low operating voltage, but it brings new problems. There fore, the multi-beam intense relativistic electron beam transmission in the multi-beam klystron is investigated by experiment and simulation. The results show that the multi-beam rotates around the center of the system due to the interaction of the multi-beam, and simultaneously the multi-beam rotates around its own center due to the space charge effect of each beam's own. All the process can result in electron beams loss.