I really interest in speaking English but the problem is my grammar so bad. So guys what do you think about that?

i think you must have course special for grammar

I think this goes without saying, but if you want to be fluent in both spoken and written english, you just need to practice, practice and practice. Write more, speak more, and if you can, try getting acquainted with a native english speaker either online or in real life. Watching shows or youtube videos in english can help as well, you'll be accustomed to what correct grammar should be like. With enough practice, you'll get the hang of things and speaking/writing fluently with correct grammar should come naturally. Hope this helps :)