Based on the autonomously designed sudden expansion swirl burner and combined with the characteristics of diesel particulate filter (DPF) regeneration, fitting geometric parameters and values were determined with the orthogonal experimental design method. And the effects of main geometric parameters such as the sudden expansion ratio, length‐diameter ratio and position of air supply pipe on main evaluation indexes of the recirculation zone characteristics were studied with CFD. Results showed that with the geometry of sudden expansion ratio 2.0 and length‐diameter ratio 2.1 and air supply pipe located in the middle of the combustion chamber, the length of the recirculation zone in the center could be increased greatly; in order to increase the reattachment length, the sudden expansion ratio should be 1.5–2.0 and the length–diameter ratio should be larger and the air supply pipe should be closer to the fuel spray nozzle; and the swirl intensity was mainly depended on the length–diameter ratio, which could be effectively enhanced when the length–diameter ratio ranged from 2.1 to 2.4. It provides beneficial references for the research of complex flow field in sudden expansion swirl burner and porous medium. © 2018 American Institute of Chemical Engineers Environ Prog, 37: 1901–1907, 2018