I'm new here. Although I have learnt English for many years, I still can't use English words correctly and properly sometimes. I can't speak just as a native English speakers.
How can I improve this situation?
Listen and practice, Jessie-- there's no substitute. From your post, it appears that your English is already pretty idoiomatic, so it's just a matter of time and commitment. If you don't have access to any live native speakers, work with TV, movies and tapes.
And we'll be glad to help you here with any questions you may have along the way.