A new method to analyze the transient response of a gas sensor is proposed. For the analysis of the sensor dynamics, the actual rapid gas concentration change during the measurement of sensor transient response should be obtained. Therefore, the distribution of the gas concentration around the sensor is visualized using the white smoke of joss sticks, and is measured as the brightness of the CCD camera image. The measured sensor response is found to be well described by a model with two phases, such as the response and recovery phases, and their transients in the two phases are expressed as second order linear systems. The results show the feasibility of estimating the sensor response from the visualized gas distribution image.