Double entry (China>Mongolia>China)

Hello, I have a doubt, I will go from Thailand to Mongolia and back through China (Erlian-Zamyn Uud land border), i.e. Bangkok>China>Mongolia by land>back to China by land>Thailand. For the flight ticket requirement, can I attach my first entry flight (Bangkok to China) and second exit flight (China to Bangkok) without attaching any China>Mongolia>China exit-entry tickets? Thanks.