I'm Australian Citizen, will transit Guangzhou for about 17 hours, do I need visa to go out of the airport?

Yes, you need a China transit visa (G visa) to go out of the airport for 1 day visit in Guangzhou. If now it is inconvenient to obtain a G visa, you can try to apply for 24 hours stay permit when you arrive at the airport, once you get the stay permit, you can leave the airport, otherwise, you have to wait in the airport for next flight.