In this paper, a new method for recovering gas absorbance shape using wavelength modulation spectroscopy is proposed. We have mathematically proven that the gas absorbance shape can be directly recovered using the data of X and Y components of odd harmonics, regardless of the value of the modulation depth. The transitions of NH(3) near 1531 nm are selected to recover the absorbance shape using numerical simulation and experimental technique. The simulation and experiment results show that our proposed method can simply and accurately recover the gas absorbance shape.