Guild Wars 2

I want to craft the melee back item in the mystic forge for my guardian but i cant find which one i need to craft for my class.

Have you looked through the wiki?

http://wiki.guildwars2.com/wiki/Back_items

http://wiki.guildwars2.com/wiki/Gallery_of_back_items

i have but it dosent tell you which one is melee or other classes

There is not specific back items for melee or range. Simply craft those with the stats that you feel would benefit your play-style the most.

http://wiki.guildwars2.com/wiki/List_of_ascended_equipment

This will list the stats of each back piece that is craftable in the forge. Books have defensive infusion slots, and quivers have offensive infusion slots.

Back items are a bit unique sharing both characteristics of armor pieces and trinkets.

They do count as armor cause the can be visable and can be damaged.
But like trinkets, there is no armor class restriction. So an accountbound backpiece like the sclerite back can be used on a warrior for a while, then put into the bank and picked up by your ele.