The present disclosure provides a molding system for preparing a fiber-reinforced thermoplastic composite article. The molding system includes: a molding machine; a mold disposed on the molding machine and having a mold cavity for being filled with a composite molding material including a polymeric resin and a plurality of fibers; a processing module configured to generate an anisotropic stress distribution of the composite molding material in the mold cavity based on a molding condition for the molding machine; and a controller coupled to the processing module and configured to control the molding machine with the molding condition to perform an actual molding process for preparing the fiber-reinforced thermoplastic composite article. The anisotropic stress distribution of the composite molding resin is generated based in part on consideration of an integral effect of an elongational viscosity and a shear viscosity of the composite molding material.