How can I go back to Australia after five years in Australia without being punished?

You can go directly to the local immigration office to explain the situation, and someone will arrange for you to return to China immediately. If the journey is far away, you can choose the nearest police station and deal with it immediately. If you have no bad criminal record, you won't go to jail. If you fail to file tax returns at work and are found out where you work, ATO of the Australian Taxation Bureau may recover the tax owed. But this is only a hypothesis, and the probability is not great.