ConnectivityManager class has tethering API methods but those methods are not visible in SDK.
But tethering methods exists in ConnectivityManager class and they works properly.
I used java reflection the standard java feature.
For using those methods, do as following.
1. Get ConnectivityManager class
Object obj = getSystemService(Context.CONNECTIVITY_SERVICE);
2. Find "tether" method on the object
Method m = obj.getClass().getDeclaredMethod("tether", String.class);
3. Invoke that method: When invoke the method send tethering interface usually 'usb0'
If you want to turn off the tethering connection, you simply invoke the "untether" method in this way.
I hope this information helps you.