Preprocess

Save the code as 'InterfaceResidues.py', then put it into your pymol Working Directory.

Detailed procedure

1. File->Run Script..., selected the 'InterfaceResidues.py' file.
2. Load the model, color the model by chain.
3. Remove waters in the model if waters do not influence the interface.
4. Run get_chains $objSel in command line to get the chains in the model.
5. RuninterfaceResidue $objSel, chain $A, chain $Bin command line to get the residues in the interface, the residues will be saved in the new generated object '(interface)', rename the object before run the command to get the residues in other interface.
6. Analysis the polar contacts: Actions->find->polar contacts->between chains

Reference

1. InterfaceResidues - PyMOLWiki
2. Get chains - PyMOLWiki
3. Pymol - 分析蛋白-蛋白相互作用界面_哔哩哔哩