Abstract: The porosity of gelled cement slurry is one of the important parameters in evaluating the gelling performance in the process of cement slurry gelling. This article compared and analyzed the gelled cement slurry and soil in macro and micro scales by means of qualitative analysis and experimental demonstration, and the result shows that these two have similar ‘framework-pore structure’, both showing certain porosity and permeability. Therefore, by introducing the method of soil porosity testing in soil science, and combining the hydration properties of gelled cement slurry, the drying method in the soil porosity test principle is changed to freeze drying by liquid nitrogen, vacuum negative pressure drying or heated and dried after hydration is terminated by soaking in absolute ethyl alcohol which can inhibit hydration. And research was conducted on the porosity of slurry at specific hydration time, which provides reference for detection of porosity of cement slurry.