Abstract: Based on the theory of Hele-Shaw and generalized Non Newtonian fluid constitutive equation, the flow mathematical model of injection molding of fiber reinforced polymer is established. Coupled with the RSC orientation model injection molding of fiber reinforced polymer is simulated by Moldflow software in rectangular mold. The results show that Along the width direction, the fiber orientation degree on both sides of rectangular mold is higher than orientation degree of the central plate; Along the flow direction, fiber orientation is poorer in the entrance section and the flow terminal piece, while fiber orientation is better in the middle piece. With the temperature of melt increasing, the fiber orientation value increases first and then decreases. Flow rate has little effect on the fiber orientation. And with the increase of injection time, fiber orientation value increase.