The sudden weakness of the legs needs to be treated according to the specific causes. 1, there may be cerebral infarction and cerebral hemorrhage, so it is best to go to the hospital for a CT examination to see whether it is a bleeding lesion or an infarct lesion, and then cranial vascular intervention according to the condition, usually to perform interventional thrombolysis or to remove the embolus. If there is bleeding, spring coils can be placed to block the bleeding of the cerebral vessels, playing a good therapeutic effect, if the amount of bleeding is relatively large, you need to perform craniotomy to clean out the bruises and place drainage. 2, may also be due to injury to the leg muscles, patellar tendon, meniscus and patella, because after the injury, when the leg is walking, it may lead to further injury to the location. This can lead to significant pain and a subconscious protective effect on the body, resulting in sudden weakness of the leg. If there is a large injury, surgical treatment is usually required, such as arthroscopy of the knee to repair the meniscus, and if there is patellar tendon, patella and muscle damage, external fixation in a cast or brace can be applied for about 3-6 weeks, and then the external fixation can be removed for functional exercises.