What is the reason for Australia's refusal?

The refusal of an Australian visa means that the visa officer is not satisfied with your personal data and is afraid that you may not be able to return to China after going to Australia. However, this is normal, because every visa officer assumes that every applicant has an immigration tendency, and even if the information is good, there is the possibility of being refused a visa.

You need not worry too much. You can sign an Australian visa at any time after it is refused, but it mainly depends on whether your binding force is stronger than last time. As long as the binding force is enhanced, it can be signed at any time and it is entirely possible to pass.