The invention discloses an automatic ticket selling/ticket checking method and system for public transit and relates to the computer communication technology. The method includes the steps of firstly, by a server, detecting whether payment is completed or not after the server receives a ticket booking request, and if so, generating and storing the corresponding relation between a user ID and credential coding information, wherein the credential coding information comprises a ticket code and the information of a preset entering station and a preset exit station; secondly, by the server, transmitting the credential coding information to the storage of the station-entering gate machines of the preset entering station and the storage of the station-exiting gate machines of the preset exit station; thirdly, performing station-entering ticket checking, to be more specific, by the corresponding station-entering gate machine, reading the credential coding information, comparing the credential coding information with the locally-stored credential coding information, and opening the station-entering gate machine if the read credential coding information is matched with the locally-stored credential coding information; performing station-exiting ticket checking, to be more specific, by the corresponding station-exiting gate machine, reading the credential coding information, comparing the credential coding information with the locally-stored credential coding information, opening the station-existing gate machine if the read credential coding information is matched with the locally-stored credential coding information, and processing the credential coding information as unavailable station exiting in the storage of all station-existing gate machine of the station; keeping the station-exiting gate machine closed if the read credential coding information is not matched with the locally-stored credential coding information. By the automatic ticket selling/ticket checking method and system which is efficient and safe, paper-free ticket selling/ticket checking of the public transit such as subways, light rail vehicles, streetcars, city BRT, suspension aerial rail vehicles and trains.