We will travel in late November to early December. What will weather be like? Clothes should wear?

It depends on which city you're going to visit, the weather varies much from South China to North China.

As for Beijing and Xian, the weather will be cold at time, because it is the winter time for both of the cities. You need to take the coats and thick sweaters. If you are afraid of the cold weather, the down jackets are necessary
For Shanghai, the weather is OK with an average temperature about 10 to 15 C. The temperature difference is big between mornings and afternoons. Besides, it may humid at that time. Thick coats and thick sweaters are necessary. If you are afraid of the cold weather, I advise you to take the down jackets also.
The cities along the Yangtze River have the similar weather as Shanghai, so you can take the same coats.
In a word, thick coats and sweaters are necessary when you come at that time.