Abstract: The delayed impregnation of dual-scale porous fiber preform during unsaturated flow process presents a challenge for the molding theory and simulation method which based on the assumption that the region nearing the flow front was completely filled and the flow was saturated during the filling process. Combined with sink function, the numerical simulation of unsaturated filling and infiltration for liquid composites molding (LCM) was realized by control volume/finite element (CV/FE) method, and the validity of the results was proven by the comparison of experimental results under the constant pressure, and the influences of injection pressure, flow rate and fluid viscosity on the unsaturated filling and infiltration characteristics of dual-scale porous fabric were also discussed. The results show that the numerical results are reliable and can be used to analyze different factors' impact on unsaturated flow characteristics of dual-scale porous fiber preform within permissible error; and the length of unsaturated region isn't constant during the whole filling process in fiber fabric which experiences four stages; pressure, flow rate and viscosity have different influence on unsaturated flow characteristic; the research results have guiding significance on appropriate manipulated injection conditions and fluid characteristic to realize the fully impregnation of dual-scale porous fiber preform.