OP registered about 1.5 years ago and only has 15 posts--that might be part of the problem. On the other hand, I bet he's got more accounts than just this one.
Also:
But I think my afford isn't so good to get merit quickly as I am working hard though I am not getting any merit because of my posts.
If you write English like the above, it isn't likely members are going to shower you with merit. You might have more luck on one of the local boards. In any case, earning merit isn't rocket science--you just have to write posts that are interesting or funny or otherwise catch the attention of members with merit to give. And you've obviously been a member of bitcointalk for a while, so this is something you ought to know already.
As I've suggested in the past, try taking a look at the post history of members who've earned a lot of merits, see how they're doing it. Part of it depends on which sections you're posting in, but mostly it's post quality (note:
not post length).