Abstract: In order to solve the problem that the silica sol shell is easy to crack during handling and dewaxing, Polyamide 66(PA66) fibers were mixed into sand material as reinforcing material at room temperature and pore former to prepare composite shell with different PA66 fiber contents. The effects of PA66 fiber content on the flexural strength, permeability and porosity of the composite shell were investigated. The mechanism of PA66 fiber affecting the properties of silica sol shell was analyzed. The research shows that the mixing of PA66 fiber significantly improves the flexural strength and porosity of the composite shell at room temperature. With the increase of PA66 fiber content, the flexural strength and permeability of the composite shell increase at room temperature, and the flexural strength increases first and then decreases after baking. When the mass fraction of PA66 fiber is 0.75wt%, the flexural strength after roasting of the composite shell is 7.94 MPa, which is not much different from that of the composite shell without PA66 fiber. But its normal temperature flexural strength reaches 4.80 MPa, which is 32.21% higher than that of the composite shell without PA66 fiber. The permeability and porosity also increase to 4.2 and 22.77%, which are 90.91% and 13.35% higher than that of without PA66 fiber respectively.