I work in Shanghai and haven't paid social security for half a year. Can I renew it?

Of course, this is possible. If you stop paying for half a year, there will be no way for medical insurance. If you want to start paying social security, no problem. You can keep paying. It will automatically accumulate years and months, which is no problem. If you used to work in Shanghai and then work in other places, there is no way out. This kind of social security can't continue, so you have to pay it again because they can't connect.