Same time periods.
Both male lead are soldiers (one in air other one in land)
They both have romance and side couples but main focus is war and people.
They both mention family and friendship relationships and how it is affected by war.
Battle of Changsha has less political mentions and propoganda.
Battle of changsha has more tragedy but acting and cinematography better.

They tell about the same time period and even some places are the same. Both mentions on education but Youth in the flames of war's main focus is on education and have less battle scenes. Both of their main focus is not romance but war and political situation. Both have bromance. The tension between nationalist and communists are mentioned in both.

The stories happen in similar times but from different aspects. They both focus on common people's lives and we see character development. Both of them feel realistic but Battle of Changsha is more tragedic.Both have romance but not heavy and have different focuses.