Abstract: Long glass fiber(GF)/polyurethane(PU) foam composites were prepared by variable fiber reinforced reaction injection molding. The influences of process parameters on the impact property of the composite were studied by orthogonal experiments, and the impact fracture morphology of specimens was observed to analyze the causes for microscopic defects forming in the composite. And process parameters were optimized. The results show that fiber content, mixture temperature, molding time, mass ratio of material A to B had a significant effect on the impact strength, while mold temperature and fiber length had little effect. When the fiber length was constant, the impact strength of composites increased firstly and then decreased with the increase of fiber content. When the fiber mass content was 30wt.% and the fiber length was greater than 25 mm, the impact strength of composites was unstable and fiber aggregation, large vacuoles, lean burn and other defects happened easily in the composites. The best molding process parameters were the fiber content 25%, fiber length 25 mm, mold temperature 45 ℃, mixture temperature 50 ℃, molding time 12 min, mass ratio of material A to B 1∶1.80.