The vapor infrared transmission spectra of varied concentration of lewisite-1 were measured by a long-path FT-IR spectrometer, and its characteristic frequencies are 814, 930, 1 563 cm-1;their infrared absorption cross section (σ) were determined using Beer-Lambert law. The corresponding σ values are 3.89±0.01, 1.43±0.06, 4.47±0.05(×10-20 cm2·molecule-1). Two little teeny peaks, 1 158, 1 288 cm-1 were found in the measured spectra. Density Functional Theory (DFT) was applied to calculated the infrared spectra of lewisite-1, -2, -3 on a b3lyp/6-311+g(d,p) level by Gauss09 package. The vibration modes were assigned by Gaussview5.08. The calculated spectra and experimental spectra are in good agreement with each other in 600～1 600 cm-1 range, for the Person’s r is 0.999 1. The calculated spectra also showed three characteristic frequencies (293, 360, 374 cm-1) related to As atom. 0.977 was a scaling factor we determined for lewisite-1 through least-square error and its performance to scale lewisite-1, -2, -3 was acceptable. The results of this work are useful for monitoring environmental atmospheric concentrations of lewisite.