The invention discloses a method for measuring gas temperature based on single spectral line TDLAS, which is applied to a system for measuring gas temperature based on single spectral line TDLAS and mainly comprises the following steps of dividing the same laser beam into two laser beams, acquiring calibration parameters by using a standard gas pool, measuring the temperature of gas to be measuredby using the calibration parameters and the like. Compared with the prior art, only one diode laser is needed to measure the temperature of the gas, an extra high-precision etalon is not needed to accurately calibrate the wavelength of the absorption spectrum, and the method is especially suitable for the condition that the distribution interval between spectral lines is very long under a low-pressure condition, such as a hydrogen fluoride chemical laser, a deuterium fluoride chemical laser and the like.