For reducing the exhaust noise in a radial rotatable diesel particulate filter (DPF), the finite element method was applied to establish the acoustic model. Depending on the model, muffling characteristics and transmission loss curve were gotten. By grey relational analysis, the effects of structure parameters on muffling characteristics in the radial rotatable diesel particulate filter were studied. The result indicated that the radial rotatable diesel particulate filter was capable of muffling. And the high frequency muffling effect, which the average magnitude was about 20 dB, was obviously stronger than the low one. The result also showed that diameter ratio and the expansion cone angle were two major influencing factors of muffling characteristics in radial rotatable diesel particulate filter. It helps to improve the muffling ability by using the smaller value of each factor.