Why is the weather in Australia opposite to that in China?

Because China is in the northern hemisphere and Australia is in the southern hemisphere.

The earth is rotating and revolving "leaning". When the direct point of the sun is in different hemispheres (northern and southern hemispheres), the earth absorbs different solar radiation, so the heat received by the earth's surface is different, resulting in temperature differences. .When the sun shines directly on the Tropic of Cancer (that is, the Northern Hemisphere), the northern hemisphere receives more heat, and the mid-to-high latitudes of the northern hemisphere experience summer; while the southern hemisphere receives less heat, and the mid-to-high latitudes of the southern hemisphere experience winter. Vice versa.