I think your issue is getting the two bent parts to match? Assuming you have two pieces of sheet metal created in ordered. Bend one of them up. Then use the edges of one piece to make sketches for the other sheet to bend.
The situation is... i create a sheet metal in ordered and then by using add body function, i created another sheet metal on top of the first sheet metal part. In order to bend/rebend I need to use bend function to bend it but I want to bend both body at one time. Is there anyway to do it? Or should i do this in assembly? For now I can do this one by one but it will consume me a lot of time.
OK, I understand Your request.
So my way would be to first have one single sheet model (body 1 and 2 together) which will be modeled as You need it and then use the split body command to create two associative shee bodies out of it.
This should be Your last feature and everything You do before will be done for both elements
The real problem is that sheet metal bends are always assumed to be in the K plane (most call it the bend axis).
In this case, you want a bend center to live outside the sheet's thickness (K outside the range of 0-1)
To do this, you will have to manually adjust the bending location to fake out where you want the bend line. I would just use an include from the other sheet metal as the bend line and do an inside bend. Then it will fit right up and you can get the required flat patterns.
This mean that you create one sheet metal and then create another one sheet metal, then you union this two body together? after that you use bend command and last step is split it again? Is this what you mean?
I have try to union two sheet metal body but failed to bend it even it is already in one body.
The premise of "sheet metal" is that the thickness if uniform, mainly for the purpose of bending calculations. Once outside that limitation.....it become a part and no longer sheet metal. My guess is there is no way around this. Now your part still only contains two different thicknesses. Perhaps once you move to part, then break the results apart by total thickness. Perhaps the union and uniform thickness commands can come into play.
Unfortunately, I don't know any direct ways to do this, but there is a modeling method what supports it.
Here is a short video about steps:
Important! You have to publish multibody to make flat patterns from each model.