A sensor was proposed to measure temperature, concentration and pressure of the atmosphere based on scanning wavelength modulation spectroscopy. The method using 4fpeak/2fpeak and 2f/1f signals of H2O spectral lines was analyzed and the sensor design program was studied. Frequency division multiplexing technology is adopted to measure gas parameters of static cell in the temperature range of 300~1 200 K using the two H2O spectral lines (7 429.72 cm-1 and 7 454.45 cm-1). Experimental results show that the iterative algorithm has rapid convergence rate and high accuracy. The measured gas temperature, pressure and concentration of H2O are consistent with the predicted value with the largest relative errors 4%, 6% and 6%, respectively.