Is there any free solution to host a unity server for my game? I searched but i can’t find any free host for my game. Do you know one?
As far as I know, there aren’t any free hosting services, especially not long-term. Amazon allows use of their servers for free for 750 hours (Secure and resizable cloud compute – Amazon EC2 – Amazon Web Services), but I have no clue if those servers are suited for game use, as they are advertised primarily for websites.
If you don’t actually need a server and just want to connect players so that one of them can serve as a host, then you can make user of the Unity Master Server (http://docs.unity3d.com/Documentation/Components/net-MasterServer.html).
Neither of these suggestions are appropriate for any sort of commercial use.