Sometime hamsters, like people, decide that they just don't like each other... All I can suggest is giving them more space. Sometimes a bigger habitat will keep them from feeling infringed upon by the other... It may be a passing phase, or you may eventually have to separate the two of them.

 Did you buy your hamster in the same day if not they will not be compatible to each other if you buy it on the same day they will not fight..
 
hope i help you