Abstract: A series of S-band dummy loads are developed by microwave Group these years. After the simulation and optimization for the S-band series of dummy loads in CST, the simulation results show that all the dummy loads achieved a voltage standing wave ratio less than 1.04 as well as a frequency bandwidth more than 100 MHz (to satisfy voltage standing wave ratio less than 1.1). All the fabricated products of the mentioned dummy loads achieved a voltage standing wave ratio less than 1.05 in low power microwave test. Among which the 14-rod high power dummy load was tested for high power performance in South Korea, where VSWR of 1.093 was tested with a pulse repetition frequency of 60 Hz as well as a pulse width of 1 s and a klystron output power of 50.7 MW. The working state of the dummy load was stable. The other dummy loads mentioned were all assembled on accelerators domestic or abroad, all of which were very stable and reliable after a long time operation.