The invention belongs to a testing method of permeability of porous materials, in particular to a testing method of external permeability of a
fiber fabric surface and a testing mold. The method comprises the following steps: firstly, laying
fiber fabric to be tested into n numbered steps on a mold panel, and then, sealing to form a mold cavity; carrying out
vacuum pumping treatment, measuring and recording distance Ln between each step surface and the mold panel, injecting fluid for testing by utilizing vacuum negative pressure, and recording time tn for the flow front of the fluid for testing to reach each step surface; and drawing a
linear relation graph of tn and the square of Ln, fitting to obtain a slope k, and then, calculating the external permeability K of the surface of the
fiber fabric to be tested according to the formula. The testing mold comprises a mold panel and a
storage tank, wherein the mold panel is fixedly connected above the
storage tank to form a sealed containing cavity, micropores communicated with the sealed containing cavity are arranged on the mold panel, and a liquid flow channel communicated with an
external liquid injecting
system is arranged at the bottom of the
storage tank. The invention has the advantages of simple operation, high accuracy, strong applicability, low cost, and the like.