Do I need a return ticket from Changsha to Bangkok?

You need a round-trip ticket from Changsha to Bangkok.

According to the regulations of the Immigration Bureau of Thailand, all foreign tourists going to Thailand need to provide valid return air tickets or continue to the next destination. This is to ensure that tourists will not stay in Thailand, and it is also an important auditing standard for the entry qualification of tourists by the Thai Immigration Bureau. So Changsha needs a return ticket to Bangkok.

In addition to the return ticket or the ticket to the next destination, the Thai Immigration Bureau may also require tourists to provide other supporting materials, such as hotel reservation certificate and travel itinerary.