A gas detection and cleaning system for a vehicle is disclosed and includes an external modular base, a gas detection module and a cleaning device. The gas detection module is connected to a first external connection port of the external modular base to detect a gas in the vehicle and output the information datum. The information datum is transmitted through the first external connection port to a driving and controlling module of the external modular base, processed and converted into an actuation information datum for being externally outputted through a second external connection port of the external modular base. The cleaning device is connected with the second external connection port through an external port to receive the actuation information datum outputted from the second external connection port to actuate or close the cleaning device.