我的NSW駕駛証已有四年,是否過了時間不能續期??

Do you mean you want to renew your driver licence? If you want to renew you NSW licence is easy, even though if it is expired.
I think you only have a Silver licence right? If you have a Gold licence, you will not get back your Gold licence after it had expired. You only will get back a Silver licence. However, if your Silver licence has expired, you will get your Silver licence again. All you have to do is to prove that you were not in Australia during that period, show RTA your passport. Then they will update your driver licence again. Of course you need to bring your old licence with you.

I just renew my licence last Easter back in Sydney. I am staying in HK now.

Hope it can help.

You can still renew it within the 2 years after it expired. I have asked RTA before.

http://www.rta.nsw.gov.au/licensing/renewingalicence/index.html

Please check the above link. You may renew your drivers licence.