What do you mean by national combined transport? Is it free?

It is not free. According to Ma's inquiry, Honeycomb Travel Network shows that.

1, national through transport is to combine flights of different airlines to realize nationwide route connectivity, so that passengers can reach another city from one city. What is important is that they can cross different flights of multiple airlines, buy air tickets and check in on the same trip.

2. Tickets are required for national combined flights, and there are no free flights.