The sudden weakness of the right leg is mainly due to three factors: First, we should consider whether there is any trauma. If there is trauma and there is muscle strain, it can also cause weakness of the leg muscles. Second, consider the vascular factors. If there is a blood clot in the veins and arteries of the lower limbs, it can also cause muscle weakness in the legs. Therefore, it is time to have ultrasound of veins and arteries of lower limbs to clarify whether there is thrombosis. Third, consider the nerve factor, that is, the compression of the lumbar nerve can cause muscle weakness in its innervated area. If the lumbar disc herniation compresses the nerve and favors the right side, it may cause muscle weakness in the right leg. Therefore, the sudden onset of weakness in the right leg should consider the three factors mentioned above: i. Trauma. Second, vascular embolism. Third, neurological factors, which are most commonly known as lumbar disc herniation, etc.