orcad Capture:hierarchy design problem

In my design, I use two instances of 1 block in 1 page. The block has a bus port.
How to distinguish every net of the bus port of instance?

The idea of having hierarchical block is not to show all bits of the underlying schematics. In this case of Half adder, A0 and A1 will not be shown in hierarchical block. But when you connect this bus to any other device (a different symbol other Half adder also), whose Bus name also follow the same endian structure (big endian or little endian), respective bits will get electrically connected. Meaning A0 of one block will be connected to A0 or B0 or C0 etc of the second block. Conversely if you want to do a bus reversal, that is changing the endian order just change the bus label to A[1:0] instead of A[0:1] in one of the blocks.

In summary, there is no need to distinguish between the bits of two instances. It will be taken care by the schematics tool.

Hope to be helpful

Also if you want to make connection to few bits of BUS (in other words want to TAP out) you can achieve the same by placing bus entry and connecting wire with that. Make sure that you place appropriate bit name on wire as net alias for completing the connection.