Hi ! i want to make multiplayer game where player can join to game even it in process(like agar.io game),is it possible in photon?(sorry for my english(not my native language))
In general yes. Everything is just a question of your design. Joining a game later is just a bit more difficult since you have to recreate the current games state on the new client.
This is not connected in any way to which network stack you are using. Photon can work fine.
But be aware that multiplayer projects can get complicated really fast and ingame joining does not simplify that. Just so you know what you get yourself into.