The two-lwvel synthetic wavelength component scheme of 3. 39μm band dual-line He-Ne laser for large length interferometry without carriage guideway is tested and verified by using infrared heatwave interferometer. The principle of the infrared heatwave interferometer used in the experiment is presented. The experimental data are given and analyzed. This work provids experimental basis for the large length measurement scheme enploying 3. 39μm dual-line He-Ne laser.