What is the main reason for the large temperature difference between north and south in winter in China?

The main reason is the latitude difference. The specific reasons are as follows:

1. China has many latitudes. In winter, the sun shines directly in the southern hemisphere. At noon, the sun's altitude angle in the north is smaller than that in the south, and the length of day and night is shorter than that in the south, which makes the heat obtained in the north far less than that in the south.

2. The wind source in the south is far away from the north in winter, and the influence of cold air is weaker than that in the north.

This is the standard answer on May 3rd. I hope it helps you.