The invention discloses a device for measuring gas temperature and concentration simultaneously through a single spectral line, and also discloses a method for measuring gas temperature and concentration simultaneously through the single spectral line. The method comprises the steps: firstly employing a peak normalization second harmonic signal line style which is only determined by temperature, and extracting the temperature of gas; extracting the concentration information through employing the directly proportional relation of the amplitude of the first-harmonic normalization second harmonic signal with concentration (background is removed), and obtaining the temperature and concentration of gas at the same time. The method can measure the temperature and concentration of gas at the same time, reduces the number of needed spectral lines, is high in sensitivity, is high in precision, and is quick in response. Compared with a conventional Doppler broadening temperature measurement method, the method can be used under the conditions of normal temperature and pressure. In addition, the method, compared with a conventional double-line temperature measurement method, does not need to consider the problems of frequency crosstalk and time resolution.