You can use Face Split to split the surfaces. If you want two different bodies with one surface. You can slice the body and create two different bodies. Afterward you should use Form New Part for these bodies and be sure the Shared Topology is selected as Default. In the Model Section of the Analysis you will find out that it is just one surface with two different bodies.
Thanks a lot for your nice reply. But I think I tried the method yesterday you mentioned that using Face Split to creat two different parts with one surface. Finally I found it is not effective because I still found in the tree outline of the model it said "1 part, 1 body" although I can choose two different bodies in the original surface in the graphical window. Now I have found a good method to achieve that goal. Firstly, I create the first face using the sketch 1. Then build a new sketch 2, but the sketch must be drawn to make sure that sketch 2 and sketch 1 have shared edges. Afterwards, create the second face within the second sketch. Then in the tree outline of the model I can see it said "2 parts, 2 bodies". Finally using form new part for the two bodies so that I can achieve the goal. In the outline of model, I can see it said 1 part, 2 bodies"