This paper presents a software platform for monitoring vehicles' CO2 emission in real time. By this platform, drivers can find the relationships between the vehicle CO2 emission amounts and their personal driving habits. Therefore, drivers can adjust their driving habits in real-time when viewing the real-time CO2 emission during the driving process. Besides, the drivers can check their speeds traces and emission amount traces through this platform after completing the trip. This platform supplies significant reference for drivers perfecting their driving behaviors in real time to realize the goals of fuel saving and CO2 emission reduction.