Objective：To investigate the inhibitory and long-term protective effects of early intra-articular injection of bone marrow mesenchymal stem cells（BMSCs） on traumatic knee osteoarthritis through immune regulation. Methods：Forty-eight New Zealand white rabbits were randomly divided into BMSCs treatment group and control group. An experimental model was established using the Hulth’s method，whereby the treatment group was injected with BMSCs on the 1st，3rd，and 5th days after the model establishment，while the control group was injected with an equivalent amount of phosphate-buffered saline. Knee X-ray was performed at the 3rd and 12th weeks. Knee specimens were collected for general observation，followed by safranin-fast green staining for histological obser－vation，and the synovial tissues were taken for inflammatory factor examination. Results：Compared with the control group，the BMSC treatment group had significantly reduced cartilage wear and a clearer appearance，as well as fewer osteophytes in general observation. The X-ray showed that the joint space became narrow，but milder than that of the control group，and subchondral sclerosis was not obvious. The safranin-fast green staining exhibited a regular cell arrangement，deeper staining，and less damage on the cartilage surface. In addition，the expression of interleukin-1，interleukin-6，and tumor necrosis factor-α in synovial tissues was also significantly decreased compared with the control group in the examination of inflammatory factors. Conclusion：Early intra-articular injection of BMSCs leads to a good improvement in the general observation of traumatic knee osteoarthritis，as well as better joint space and car－tilage on X-ray and safranin-fast green staining，respectively；meanwhile，the expression of inflammatory factors is also significantly reduced in synovial tissues.