Abstract: An S-band high power microwave test bench was presented in this paper. It mainly consists of the magnetron, modulator, high power microwave transmission components, high power testing devices and protection device. High power measurement of microwave components could be carried out on the bench by using measurement devices composed of a water load and power meters. Some major parameters of microwave components could be measured, such as insertion loss, isolation and input VSWR. In addition, the bench is capable of stably operating at a pulse power of up to 3.1 MW by using a circulator and a quick response protection device. Finally, the experimental results of the bench were given.