The summer crowds would have left, and the weather is mild. Winter can be bitterly cold though the country looks very pretty covered in a blanket of snow. Avoid travelling to China during major holidays as all businesses come to a standstill.
Tourist attractions are also closed.
However, you do not need to pack a lot of warm clothing as you will be able to get some excellent down or quilt jackets in Beijing or Tianjin. In summer, the weather is very humid and hot. The lightest of clothes like T-shirts, sandals and shorts will do for daytime wear. However, bring along a light sweater in case you are going up to the hills as it can get very cold. Generally, the dress code in China is casual.