Cultural tourism has received widespread attention for its role in promoting cultural heritage and economic growth. However, there is insufficient research regarding how to verify the synergy between culture and tourism and how to ensure its sustainability in the integration of the cultural and tourism industries (CTI). This study establishes an interdisciplinary composite analytical framework from the perspective of efficiency evaluation. China, a country that has advocated the integration of CTI since 2009, is the research setting. The findings indicate that the technical efficiency of the tourism industry has increased significantly since the involvement of the cultural industry. Meanwhile, economically underdeveloped regions have opportunities to catch up with developed regions in terms of technical efficiency, and they perform better in terms of sustainable productivity growth. Importantly, U-shaped and inverted U-shaped curves were found in the coordinate systems composed of groups comprising the coupling coordination degree and the efficiency-related index, respectively. This finding reveals the existence of a running-in effect in the integration process of CTI, thereby contributing to both theory and policy-making.