Thank you very much for this website and the people replied my questions.
Here is my experiences for this exam, hope it'll help those people who are preparing this exam (Spend less money but it will take longer time).
1. I read the Head First book 3 times. The first time took me nearly 3 months. After that i found out i almost forgot everything, then I start to read the book again. The second time took me 1 month. And then i tried to start doing the mock test, but i still not confident. So i decided to read the book the third time, but this time it only took me 1 week.
2. Mock tests: I finished the HF mock test (it is free with the HF book). I also finished the free of charge mock tests listed in javaranch.
Good luck for those still preparing this SCWCD and Merry Christmas