The invention discloses a carbon nano tube film ionizing sensor and a method for detecting the concentration of a single gas based on the same. The sensor comprises a first electrode, a second electrode and a third electrode which are distributed sequentially; a ventilating hole is formed on the first electrode; a metal film substrate on which a carbon nano tube film is distributed is attached tothe inner surface of the ventilating hole; an lead-out hole is formed in the centre of the second electrode; a blind hole is formed on the board of the third electrode; and the three electrodes are isolated mutually. The method comprises the following steps of: 1) placing three sensors with different interelectrode distances; 2) exerting voltage on the electrodes; 3) measuring ion current values of the sensors; 4) forming a sample by combining the measured values and the calibration values of the concentration, the temperature and the humidity of the single gas, and constructing a gas concentration measurement database by the sample and an interpolation sample; 5) constructing a data fusion device and building a single gas concentration accurate measurement model; and 6) inputting the actually measured values of the sensors into the measurement model to obtain an accurate measured value of the concentration of the single gas. The sensor is high in gas detection sensitivity, high in linearity and high in accuracy.