Point 1, there is no problem here, it is the junction of hip and abdomen, the joint is smooth.

Point 2. Here is the problem.
The joint is not smooth here. And this is only one of many joints that are not smooth.
Only joint at point 1 is smooth. I made the cloth in one piece and detach into different body parts.
Then I have one joint smooth but others dont. Can someone tell me to correct it?

Point 3. I think there is something wrong with the polygons there.
It goes black when I render with shade. The obj at left is render without shade.

Can someone help me?

I think that at point 2 you will find vertices that are not welded. If they have slightly different locations you will need to match them up and then weld them.

I'm not sure what is happening at point 3, but it may be degenerate polygons. I have no idea how to fix those.

Thanks, Roy I made the whole cloth as a whole, and detach the polygons to different parts. I made it for the abdomen and hip, these no problem, but on other parts, the problem come out. Is that the process of detach will move the vertices? I don't move them! (I made it in 3DS max)

Sorry I'm not familiar with 3DS Max, I use Rhino. I have seen similar problems with props, but I have not tried my hand at making conforming figures yet so I'm no expert. I think that there need to be weld statements in the cr2 file that join the parts back together but I'm not sure.