Accurate calculation of spectral line profiles of a gas is very important for gas sensing. As we know, a variation in pressure (temperature) of a gas will result in the corresponding variation in temperature (pressure) of the gas. In the present paper we calculated spectral line profiles of a gas by considering the changes in both temperature and pressure. The authors found that in our case the Lorentzian profile has broader applicable ranges of pressure and temperature, and the Gaussian profile is only applicable in some extreme conditions. Furthermore, the authors found that the influence of variations in pressure and temperature has to be considered in calculating the peak values of the spectral line profiles such as Gaussian, Lorentzian, and Voigt; otherwise the resultant relative errors of the calculated peak values can exceed 0.1. The similar observations were also found for other gases such as CH4, CO2, CO, and NO, although the parameters such as wavelength, coefficient of pressure-broadening, relative molecular mass, and temperature were different.