I travel around Australia, I find some camper van hire service in Australia,i just want to know is there some camper park from Sydney to cairns for free?
I have travelled along Australia's east coast between Sydney and Byron Bay on various trips in a camper van. Sydney beaches tend to be more crowded and often require payment for parking. Camping is specifically not allowed here. There are council rangers. Do not stay for free until you are north of the Hawkesbury River.
Once you are out of Sydney, you have three basic options:-
To a first approximation, no, you will not really find any free camper parks in eastern Australia. (I'm told Western Australia has more.) Campervans need space to park, water, electricity, sewage etc, all of which costs money, so somebody has to pay for your "free" camping.
That said, there are some free campsites, they're just few and far between. This site lists a few, although it's nearly unusable since the maps are broken, while Visit NSW has a more thorough listing of paid options.
Of course, you can always just park in some random parking lot, but this is not a realistic option for more than a night or two, and dumping waste anywhere outside an approved dump station will get you heavily fined.