We present a signal-processing system developed for enhancing the sensitivity of absorption measurement based on tunable diode laser wavelength modulation spectroscopy. A signal-to-noise ratio enhancement of an order of magnitude was observed when digital signal-processing algorithms were applied to wavelength modulation spectrometers in the near-infrared，at the same time a new spectra was found by observation of CO2 near 1.53 μm. These algorithms include digital low-pass filters, multiple averages, and a least squares fit. Digital signal processing has a practical advantage over other noise suppression techniques because it is easy to implement and adapt able to all experiments.