A gas sensing method using a thin film type gas sensor is provided to calculate an exact pollution degree by compensating a reference value change of the thin film type gas sensor. A gas sensing method using a thin film type gas sensor includes the steps of receiving and averaging n data from a thin film type gas sensor to calculate a reference value and a current value(S30,S40,S50,S60), comparing the current value with the reference value, calculating a pollution degree using the reference value and the current value when the reference value is less than the current value, again calculating the reference and current values after a predetermined time lapses when the reference value exceeds the current value, and calculating the pollution degree based the calculated reference and current values(S62,S70,S72,S74,S80,S90), and displaying the calculated pollution degree(S82,S92,S100).
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