This paper proposes an efficient model for simulating fiber motion in viscous flow, especially during molding of fiber-reinforced thermoplastics. To increase the computational efficiency, the proposed model discretizes fibers as chains of fewer spheres than in the bead-chain model previously proposed by the authors, which is called the Simplified Bead-Chain Model (SBCM). In addition, in order to make the proposed model reproduce the results of the SBCM, correction factors applied to forces exerted on each sphere are newly derived so that the equation of motion of a fiber for the proposed model can be equivalent to that of the conventional model. Simulations of rigid and flexible fibers in simple shear flow are first performed to compare the fiber motions between the two models. The proposed model reproduces the results of the SBCM closely for cases of both a single fiber and suspensions containing multiple fibers. Finally, fiber orientation behavior during injection molding in a simple-shaped plaque is simulated. The results obtained with the proposed model shows good agreement with those of the SBCM but at lower computational cost.