In order to improve the accuracy of methane gas concentration detection by tunable semicondu- ctor laser absorption spectroscopy (TDLAS) technology, a noise reduction method of complementary ensemble empirical modal decomposition (CEEMD) combined with permutation entropy and S-G filtering has been proposed for the problem of noise interference in the directly absorbed signals during the detection process, and permutation entropy and S-G filtering are used to solve the problem of CEEMD decomposition with the occurrence of spurious components and noise residual noise in the CEEMD decomposition. By simulating different noise contents of methane gas absorption signals and comparing with the traditional CEEMD method and wavelet transform method, the effectiveness of the proposed method is verified, which provides the basis for the subsequent experiments. The experiments show that the proposed method can effectively reduce the noise interference in the gas absorption signal and improve the measurement accuracy of the system, compared with the comparative methods, with the highest goodness-of-fit of 0.991 1 for the Lorentz line fit of the absorption spectrum curve, and the goodness-of-fit of the absorption spectrum amplitude to the methane gas concentration of 0.998 46.