A method for quickly calculating mileage includes the steps: A, receiving report data from a vehicular terminal and updating data center according to the report data; B, receiving an inquiry request which includes a vehicle number, a first time point which is earlier than a second time point and the second time point which are requested to inquire; C, inquiring the data center to acquire a first total mileage value to which the time point that is proximate to the first time point corresponds and a second total mileage value to which the time point that is proximate to the second time point corresponds; D, obtaining a running mileage L from the first time point to the second time point by subtracting the first total mileage value from the second total mileage value. A system for quickly calculating mileage quickly is also proposed. The method and the system can calculate mileage quickly and accurately, reduce the processing burden of the data center, and facilitate the vehicle surveillance of the traffic department.