I have a model with ten parts, all in a atlas texture and share one material.
I guess there is one Drawcall, but in fact I get 8 Drawcall.
Can someone help me, How I can reduce Drawcall.
You need to have static batching (or dynamic batching for small moving parts) in order to have the drawcalls batched together as one.
Static batching is only available in Unity Pro
More information about batching you can find here:
You can also reduce your draw calls by optimising, e.g. if you have 10 separate parts but not a single mesh, try combining it manually in your 3D package, other such tips here Unity - Manual: Graphics performance fundamentals