China’s Western Development Strategy (WDS) has generated stark differences in policy environments for tourism development. Considering the WDS as a quasi-natural experiment, the paper applied an increasingly important regression discontinuity design method to tourism studies and explored the causal effect of the WDS on tourism by comparing treated and untreated cities proximal to the geographic boundary of the WDS. We prove that the WDS has caused a significantly positive effect on tourism development and is estimated to be up to 6% and vary from 5.9% to 6.7%. The mechanism analysis indicates that the WDS can affect tourism development through infrastructure construction and tax incentives.