Rainfall affects road conditions and driving environment, which in turn affects the reliability of public transportation. In order to clarify the impact of rainfall on the reliability of urban bus travel time, this paper analyzes the statistical changes of bus travel time affected by rainfall based on the GPS operating data of public transport and hourly rainfall data considering the impact of setting up bus lanes. In order to further explore the influence mechanism of rainfall on bus travel time reliability at the theoretical level, this paper constructs a bus travel time reliability evaluation model, which evaluates the reliability through three parameters including passenger reserved travel time, buffer time, and excess delay. The research results show that rainfall has a negative impact on bus travel time, leading to increased bus travel time and its volatility, and bus lanes can effectively reduce the fluctuation range. Compared with fine weather, passengers need to reserve longer travel time on rainy days to ensure that they can reach their destination on time, the reliability is reduced, and bus lanes can effectively suppress the decline in bus travel time reliability. By constructing a bus travel time reliability evaluationmodel, the bus travel time reliability evaluation system is formed to provide theoretical support for the study of bus operation decision-making and dispatch in bad weather of rainy days.