Abstract: An accelerating structure to obtain the average beam power of 10 MeV/100 kW for high average beam power industrial irradiation accelerator was developed. The results of beam dynamics studies and accelerating structure optimizations are as follows. The accelerator uses a bi-periodic standing wave on-axis coupling structure. An accelerating cavity and a coupling cavity form an accelerating structure unit. The operating frequency of the unit is 325 MHz at π/2 mode. The coupling slots were used to couple the accelerating cavity and the coupling cavity together by magnetic coupling. The SUPERFISH code was used to optimize some key parameters like effective shut impedance and Kilp factor. The PARMELA code was used for beam dynamics studies. A 2.5 keV/500 mA electron beam was injected into an accelerating structure which consists of 6 accelerating cells to obtain the average beam power of 10 MeV/100 kW. The CST-MWS code was used to design the coupling cavity. The optimization results of the accelerator consisting of 6 accelerating structure units are that the effective shut impedance is 23.9 MΩ/m, the unloaded quality factor is 29 347, the coupling factor between every accelerating cavity and its adjacent coupling cavity is 4.7%, the π/2 mode isolation bandwidth is 2 MHz, and the peak power loss is no more than 290 kW per unit.