Measurement method of two-dimensional tomography of gas temperature and H2O concentration distributions in non-uniform combustion flow field is proposed based on wavelength modulation spectroscopy (WMS). By using the measured 2f/1f signals, we measure the integrated absorbance after laser passing through the non-uniform field according to numerical simulation and iteration. Then, we realize the measurement of two-dimensional tomography of combustion flow field using the reconstructed algorithm. The numerical simulation for single Gaussian and step change distribution models is carried out with selecting two groups of spectral lines of H2O. Frequency division multiplexing technology is adopted to realize the measurement of temperature and H2O concentration distributions in the flat combustion flame. It is proved that the method based WMS has relative high reconstruction accuracy. For single Gaussian model, the reconstruction errors of temperature and H2O concentration are less than 2% and 2.5% using the lines of 7185.60 cm-1 and 7454.45 cm-1. It also can be seen that the reconstruction errors are small if the lines are sensitivity to the temperature while the reconstruction errors are big if the lines are insensitivity to the temperature. Experimental results show that the reconstruction results are agreement with the predicted values in the middle region of flame where the temperature has the tendency of continuous change, the reconstruction error is less than 3.2%. However, in the edge region of flame where the temperature has the tendency of step change, the reconstructed effect is not good because the WMS and algebraic iterative reconstruction algorithm are insensitive to field where the temperature has the tendency of step change.