High-speed railway (HSR) is a new and increasingly popular transportation mode in China bringing about a significant impact on the economy, including tourism development. This article investigates the effect of HSR on tourism development in China based on a time-varying difference-in-differences model. Cities connected by HSR in 2013 and 2014 are regarded as the treatment group, while those without HSR services until 2017 are placed in the control group. The empirical analyses cover a large panel dataset comprising 163 cities in 2009–2017. The empirical results suggest that both domestic tourism revenue and tourist number are positively affected by HSR, and the effect is stronger for the undeveloped or geopolitically less important regions such as the inland or prefecture-level cities. Other relevant determinants of tourism include the availability of airports and the number of hotels in the cities. Our research findings have important policy implications for tourism development in China with respect to HSR.