To deeply explore whether ride-hailing services directly affect road traffic crashes and whether they indirectly affect road traffic crashes by changing the usage of buses and private cars，based on panel data from 114 cities in China from 2005-2017，the multi-period DID method and the causal steps method are used to estimate the impact mechanism of ride-hailing services on road traffic crashes. The results show that the entry of ride-hailing services increases road traffic crashes by 5.6%，and this conclusion still holds after performing robustness tests such as parallel trend and Propensity Score Matching-DID. Ride-hailing services significantly reduce public transit usage by about 19.3%，thus indirectly increasing road traffic crashes by 0.71%，which indicates that public transit usage plays a mediating effect. Ride-hailing services significantly increase private car usage by 5%，thus indirectly increasing road traffic crashes by 0.14%，which indicates that private car usage plays a mediating effect. The decrease in public transit usage is an important reason why ride-hailing services indirectly increase road traffic crashes. Government departments should strengthen the regulation of ride-hailing services，while encouraging the synergistic development of ride-hailing services and public transit.