The invention discloses a method and device for rapidly measuring sidewall appearance of a micro-nano deep groove structure, which can simultaneously and rapidly measure the parameters of the sidewall appearance of the micro-nano deep groove structure, such as 
line width, groove depth, sidewall angle, 
sidewall roughness and the like. The method comprises the steps of: projecting elliptical polarized lights, which is obtained by polarizing light beams with the wavelengths 
ranging from near 
infrared waveband to 
middle infrared waveband, onto the surface of a structure to be measured; collecting zero-level 
diffraction signals on the surface of the structure to be measured, and calculating to obtain a measured 
infrared spectroscopic ellipsometry of the micro-nano deep groove structure; calculating theoretical spectroscopic ellipsometries in the near 
infrared waveband and the 
middle infrared waveband respectively by using a 
wavelength allocation modeling method, matching the theoretical spectroscopic ellipsometries with the infrared 
spectroscopic ellipsometry measured in the experiment by using a stepwise 
spectral inversion method, and sequentially extracting the groove structure parameter and the roughness parameter. The device comprises an infrared 
light source, first, second, third and fourth off-axis parabolic mirrors, a Michelson's interferometer, a planar reflector, a 
polarizer, a sample bench, an analyzer, a 
detector and a computer; and the method is a noncontact, nondestructive low-cost method for rapidly measuring the sidewall appearance.