As a strategic fulcrum for China’s deepening reform and opening up, Hainan Free Trade Port (HFTP) will implement the “four taxes and two fees” merger reform after closing the port for operation in 2025, and uniformly levy sales tax at the retail link. This innovative tax system measure poses significant impacts and challenges to China’s current accounting processing system. Based on the reference of international tax reform experience and the analysis of the adaptability of China’s accounting standards, this paper systematically constructs a theoretical framework for sales tax accounting. It focuses on the application scenarios of trade enterprises in the tertiary industry, deeply explores the accounting connection paths and industry adaptation schemes during the tax system transition, and provides solid theoretical support and feasible practical guidance for the smooth implementation of this policy.