A constitutive model and a damage effect model of short-fiber-reinforced injection-molded (SFRIM) composites are established by referring and modifying the existing constitutive model of SMC (sheet molding compound) and the aniotropic damage behavior model. And the crash simulation of bumper beams made of SFRIM composite is performed with a commercial crash simulation package PAM-CRASH in this paper. The model is coded using a user-defined subroutine of the package. Tension tests of PC (polycarbonate) and PBT (polybutylene terephthalate) containing 10 to 30 percent of glass fibers by weight and impact tests for simple-shaped beam made of SFRIM composites are performed and the experimental results are compared with the ones of simulations to verify the model established. Ultimately the possibility of substitution of SFRIM composite bumper beams for existing ones is examined.