I want to visit Shanghai and Hong Kong can i get a 7 days visa when landing?

Allen, you don't need one for HK because you enjoy 90 days free stay if you hold valid US passport. However, you should apply one for Shanghai if you stay more than 72 hours. If you fly from HK to Shanghai, stay less than 72 hours and then fly to Thailand, you might make use of the free transit to avoid applying entry permit. The premise is that your flights don't stop by any other Chinese cities.