Hardly to classify. It's just.. 21 seconds.

Ok lemme tell ye this. It's pretty easy to write something awesome which lasts 01-60 seconds. What hard, is to make a full song of at least 4 minutes worth material. Especially if you're instrumental, because people wound want to listen to diversed music to compensate the lack of vocals. Sorry, it's really hard to criticize 21 seconds.
Ok, thanx a lot i'll try to make smth that will last longer)
At least 2 minutes))
I'd say that it's a fairly good melody. Obviously, it won't work on it's own, but it could easily be incorporated into something else - maybe as the solo to a song, maybe as the intro. Might work as a vocal melody too, but I'm a bit unsure about that.

Mostly, I'd suggest building an instrumental out of it. You've got the basis, now start arranging. Create a chord progression for it, and use your melody as the "chorus" of the instrumental.
Nashag, I glad you like it!)
Thank you for this usefull tips, now i'm full of enthusiasm to continue my work on it!
But i hsve a litle problem - i'm making music from time to time
I mean sometimes i can write smth and sometimes i can't
It's all because i don't now the music theory?
Or everyone has the same problem?