My rank just gets bad even if i win (mostly i win )
So why? mY rank was 100 and now whenever i play a ranked match it makes my rank bad even if i win

It often takes a while for your rank to stabilise, it is because your rank is based upon where you are in comparison with other players, so as their elo increases, their rank increases, and as such yours goes down.

It also takes a while to update, so if you go down it's probably because your rank was showing you to be higher than you actually are; it will stabilize eventually if you keep playing.

Why D: But whyy!

If you are suggesting the current system needs changing, you're going to want to post a thread in the Suggestions & Ideas Sub Forum, found here:
http://forum.toribash.com/forumdisplay.php?f=640

If I remember correctly, you must defeat players who are higher in rank to you to actually keep going up. Just defeating random people who are lower or don't even have a rank doesn't change your rank, and you'll eventually go even lower in ranks.