Objective:To explore the effect of photobiomodulation (PBM) combined with umbilical cord mesenchymal stem cell transplantation on motor function recovery in rats with spinal cord injury.Methods:The mesenchymal stem cells were irradiated with a laser energy density of 1.5, 3, 6 and 12 J/cm 2. The optimal energy density was screened by the MTT method on the 3rd day. Before cell transplantation, 32 male SD rats were randomly divided into the spinal cord injury group, which was injected with normal saline without cells; the stem cell transplantation group, which was injected with stem cells in the injury model; the laser irradiation group, which was injected with cell-free saline and laser irradiation; and the combined treatment group, which was treated with cell transplantation and laser irradiation. BBB score and inclined plate test were performed on the 1st, 3rd, 7th, 14th and 21st day, and hematoxylin-eosin staining and Nissl staining were performed on the 21st day. Results:The laser irradiation with an energy density of 12 J/cm 2 can accelerate cell proliferation ( P<0.05). After the modeling, the BBB score of the combined treatment group was higher than that of the other groups (all P<0.05), and the motor function recovered significantly. In the inclined plate experiment, the performance of the combined treatment group and the laser irradiation group was also better than that of other groups. The results of hematoxylin-eosin staining showed that the cavity area in the combined treatment group was significantly reduced, and the inflammatory reaction was the lightest. The staining of Nissl bodies became deeper, and the spinal cord injury was significantly reduced. Conclusions:PBM can promote the recovery of motor function in rats with spinal cord injury after the transplantation of umbilical cord mesenchymal stem cells, and has an obvious therapeutic effect on spinal cord injury in rats. This study provides a basis for the treatment of spinal cord injury.