Both high-speed rail (HSR) and air transportation networks have important impacts on accessibility to cities. However, few attempts have been made to analyze the combined modal accessibility of HSR and air, especially in the case of China. To fill this gap, this study aims to measure accessibility under a combined HSR and air transportation network in China. Average travel time (ATT), weighted average travel time (WATT), and potential accessibility (PA) are employed as indicators of accessibility. The results show that inter-urban accessibility under the combined network shows a decreasing trend from the central to the surrounding region, with the level of combined network urban accessibility significantly higher than that of either individual network. Under the ATT, WATT, and PA indicators, the combined network outperforms the HSR network by 46.53%, 47.69%, and 49.23%, respectively, and the airline network by 15.49%, 13.17%, and 75.45%, respectively. In addition, the combined network shows a more equitable distribution of accessibility than that of the HSR network.

The role of the digital business environment (DBE) in the sustainable development of enterprises (SDE) has received extensive attention. This study aims to discover what factors of DBE affect SDE. The empirical results based on China’s inter-provincial panel data from 2011 to 2021 show that DBE has a dual impact on the quantity and quality of enterprises from five dimensions, digital infrastructure, digital industrial environment, digital R&D support, digital talent supply, and digital market demand, among which the digital industrial environment, digital R&D support, and digital talent supply are more conducive to enterprise sustainability. The digital industry environment, digital R&D support and digital talent supply are more conducive to improving enterprise development quality. The results of the heterogeneity analysis further show that there is a significant difference in the regional effect of DBE on SDE. Enterprises in eastern, central, and western China show a tendency to differentiate the demand for different factor conditions, such as technology, industry, and talent, in the process of development. The research in this study provides new theoretical perspectives and empirical evidence for optimising the business environment and achieving SDE.