Osteoporosis is a multifactorial related systemic skeletal disease characterized by loss of bone mass and destruction of bone microstructure, often leading to fractures. As early as more than 50 years ago, it was found that the risk of osteoporosis was greatly increased in patients with spinal cord injury (SCI). As a serious complication after spinal cord injury, osteoporosis not only brings a huge economic burden to the patient’s family, but also seriously impedes the progress of the patient’s recovery and increases the mortality rate. In recent years, there have been hundreds of studies on the correlation between spinal cord injury and osteoporosis, but none of them have found fundamental results, and many of the conclusions are contradictory to each other. In this paper, we will review the following aspects. In recent years in the study of osteoporosis after SCI, the study of mechanical properties of bone has received more and more attention. It has been found that the tensile force, bending stress, impact toughness, amount of stress relaxation, creep, and compression force, torsion force, and shear force of the femur and tibia of patients after SCI are significantly reduced. The impact toughness, compression force, and shear force of the vertebrae were also significantly low, and collagen fibers are extremely important factors affecting mechanical properties.After spinal cord injury, due to the reduction of BMD, some of the bone trabeculae were broken, so that the collagen fibers were arranged in the direction of the change, resulting in the relaxation of its stress, the amount of creep decreased collagen content, the reduction of the mechanical support capacity of the framework to provide a framework for the mineralization of the bone, so that calcium salts could not be deposited to mineralize, thus causing the bone loss and reduced biomechanical strength of bone. Muscle transmits load to bone, and after SCI muscle undergoes a series of histochemical and metabolic enzyme changes in order to strain the state of reduced activity into an atrophic state and develops a fatigue-prone phenotype, and the loss of muscle load and reduction of mechanical stimulation greatly contributes to the demineralization of bone. It has been demonstrated that if electrical stimulation of paralyzed muscles is maintained at a certain physiological level, it is likely to reduce the reduction of BMD after SCI. The reduction in bone mineralization was lower in paraplegic patients with spastic paralysis than in paraplegic patients with flaccid paralysis. The spastic state has more muscle content, and the high content of muscle tissue may reduce the metabolic abnormalities secondary to SCI patients, but whether these abnormalities are related to osteoporosis needs to be further confirmed. Muscle spasm and tension in the forced state exerts pressure on bone, which may be a protective factor for bone density. Patients without spasticity are more likely to fracture, but excessive spasticity can also lead to fractures, for example, if the patient does not have enough coordination to control limb movement in a wheelchair. to the point of increasing the chance of injury. It has been suggested that the effect of a state of ankylosis on the skeleton may be two-fold: low spasticity is beneficial whereas high spasticity is detrimental. Women are more prone to osteoporosis than men, which is related to the decrease in estrogen and activity in postmenopausal women.