Abstract: With the low-carbon mode gradually gets people′s attention,it is imperative to establish a low-carbon, environmental,low-consumption,efficient and safe mode of transportation systems.Existing studies in China and abroad focused on the target of using energy consumption or passenger turnover quantity to optimize the transportation structure. The study develops a low-carbon and optimization model for urban transit systems with the use of carbon footprint calcu-lation formula.Taking the minimum carbon footprint per capita and maximum urban transit system efficiency as the tar-gets,and using travel demand of citizens,developed urban energy consumption limits,accessibility of residents and transport capacity of all kinds of transportation modes as the constraints.The public transit systems of Beijing in 2020 are optimized using this model.The results indicate that the efficiency of new public transit systems is better than the tradi-tional one,and per capita carbon footprint drops 5.965 g/person,which is 13.7% less than the traditional one.The study results demonstrate the feasibility of optimizing the urban public transit systems through low-carbon mode.It will also en-courage the cities to adopt a low-carbon mode for their public transit systems.