Single factor analysis method was used to simulate the foaming process of asphalt with CFD software. The primary structural parameters of foaming chamber, such as chamber volume, asphalt entrance size and foamed asphalt outlet size, were taken as simulating variables. And their effects on the temperature, pressure and velocity fields in the chamber analyzed. Then the grey related degree method was applied to analyze the relationship between the structural parameters of chamber and its internal flow field. The results show that the velocity, pressure and temperature fields of the cavity are much better for asphalt foaming when the chamber volume is 2V, asphalt entrance size 0.71Q and outlet size 0.75D (V, Q and D are the basic dimensions of parameters). In the sequence of chamber volume, entrance size and outlet size, the correlation degree between the parameters and internal pressure field are 0.56, 0.64 and 0.53, the correlation degree between the parameters and internal flow velocity field 0.68, 0.71 and 0.72, and the correlation degree between the parameters and internal temperature field 0.75, 0.71 and 0.70, respectively. These imply that the asphalt entrance size has the biggest effect on the internal pressure and temperature fields of the chamber, and the foamed asphalt outlet size the biggest effect on the internal velocity field of the chamber.