Beat Making Headphones
Hello!
I starting a beat making and I need great headphone! So what do you think about KRK KNS 8400? Thanks in advance and sorry about my English, I am Serbian! 
what is your budget… style of music… etc…
Audio Technica, Sony(mdr series) Senheisser, V-Moda, Pioneer and a number of other manufacturers make great headphones… i currently use Audio Technica m35x for general use and my trusty Shure 440’s they seem to do the trick.. although i have a pair of mackie monitors to fall back on
Budget
My budget limit is 350$! But I want Studio Monitors and Headphone from same brand (for example KRK or JBL or Yamaha)! 
Generally, when producing and mixing music, monitors are the preferred solution. When headphones must be used, some consideration must be made for how that changes the way music is perceived. This article has a reasonable discussion of those differences.
In general “open” headphones will give better results than “closed” headphones…especially if there is significant stereo content.