How to draw this middle part?

[kingston123]

I successfully completed outer part of the diagram but failed to construct middle part:

I am using CATIA V5R19 Software to construct it.

 

[MrCATIA]

A picture of your part would be helpful.

The opening in the middle can be done with a Pocket based on a sketch. When you make the sketch, all the curves need to be constrained to the outside geometry and/or the holes. You could use the Offset tool, or you could just draw new arcs and circles and constrain them concentric to their outside partner. Either method will require a lot of trimming - maybe that's where you failed? Use the Sketch Analysis tool to check for a 'Closed Profile'