how i can bake one object per one texture ?

What Unity version have you got ?

If you use Unity 3 I don't think you can do this. I work a lot on lightmaps and you can't say those in this one or those in this one. Except if you bake them one by one and you manage their lightmaps by code (and even with this I don't really think you can).

If you use unity 4, you can bake the lightmaps by selection so you can select what you want in one lightmap then bake. Then select another part of your scene and do bake the selection again and this msut work.

In unity 3 "bake selected" erased previous baking session but in Unity 4 it didn't. I never try to bake with Unity 4 I just read release notes so you can try this ;).

yes i tried with unity4 but i have this problem uv auto arrange i can't control my texture ( i mean 1 object 1 texture ) i have question in here: how i can use uv channel 2 in 3dsmax to bake lightingmap in unity3d ? i create channel 2 in 3dsmax but when i import fbx in untiy3d and bake map uv auto rearranged( now uv not same in 3dsmax i created)

i not check (Generate lightingmap uv) in fbx

now how i can use uv channel 2 i created in 3dsmax to bake lightingmap in unity3d ?

http://answers.unity3d.com/questions/459336/how-i-can-use-uv-channel-2-in-3dsmax-to-bake-light.html