The quality of the liquid crystal cell surface can affect the performance of the spatial light modulator. In order to accurately measure the liquid crystal cell surface, a low coherent carrier frequency interference method is proposed. Illuminating with a low coherent extended light source, forming a localized interference between the reference light and the test light, and adding a suitable carrier frequency by controlling the tilt angle between the reference surface and the surface of the liquid crystal cell, the carrier frequency interference fringe to be tested is obtained. The upper and lower surfaces of the air layer of the empty liquid crystal cell form a background interference fringe, so that a single carrier frequency interference pattern with a set of interference fringes is collected in the CCD camera. The frequency information of the background and the interference fringes is filtered by the spatial Fourier transform method, and the surface data of the fringes to be tested is extracted and restored. The surface of the liquid crystal cell made by dislocation bonding of two glass substrates was tested. The peak-to-valley value PV of the surface is 8.28λ, and the root mean square value RMS is 178λ. Comparative experimental results conducted by the method and ZYGO interferometer indicate that the differences of PV and RMS are 0.02λ and 0.004λ. The results obtained by the two measurement methods are consistent. The method can overcome the problem of multi-surface interference and measure the liquid crystal cell surface precisely.