Using a panel data set of 36 cities in the Sichuan-Chongqing Economic Circle in China from 2011 to 2019, this study adopts a spatial difference-in-differences (SDID) model to analyze the effect of high-speed rail (HSR) on urban tourism development. The results show that HSR operation can significantly promote the development of urban tourism. The spatial autoregressive parameter is 0.3, indicating a positive spatial spillover effect on tourism flows. Our conclusion still holds after a series of robustness tests, including using the PSM-SDID model and placebo test. Second, we find that the impact of HSR on tourism increases by year, peaking in the third year. Third, HSR has a greater impact on cities with less developed road transport and immature tertiary industries. Finally, we confirm the substitution effect between HSR and air transport.