The computer simulation to predict the effect of mold geometry on the fiber orientation in the injection molding filling process has been developed. Finite element/control volume method was used to analyze the flows in the complex geometries and the particle tracing method was adopted to predict the fiber orientation distribution by using the equation of change for orientation tensor considering the interaction between fibers. As the results of numerical simulation, the fibers near the side walls and inserts tend to align along them due to shear effects. When two separate fluids join passing around inserts, the fibers near the weldlines tend to orient parallel to the flow. In addition, it was confirmed that the fibers in converging flow tend to align to the flow direction while the fibers in diverging flow are oriented perpendicular to the flow. The skin-core structure which indicates two different layers by the effect of the shear gradients caused by upper and lower walls could be predicted numerically by considering the velocity gradient through the gap width. It was confirmed that the fibers in the skin layer are oriented parallel to the flow and those in core layer are oriented perpendicular to the flow. As the fiber/fiber interaction coefficient increases, the fibers tend to be oriented in random distribution state.