Abstract: In order to effectively control fabric quality in the wet processing such as dyeing， printing, finishing and design a fabric which has better thermal-moisture comfort, this paper has proposed the theoretical basis and method for measuring capillary radius distribution along fabric plane based on the equilibrium between Laplace pressure of concave in front of capillary liquid and hydraulic pressure of liquid column by weight classification differentials. The capillary radius distribution of cotton fabric is measured with self-made laboratory instruments, and capillary radius distribution histogram, distribution curve and cumulative curve are obtained and all of them exhibit good reproducibility. It is found that warp-weft density of the fabric has significant impact on the capillary radius distribution, average radius and radius with maximum ratio.