The properties of ceramic membrane substrate mainly affect the selective layer membrane on several aspects, such as operating condition and permeability. In this paper, a new type of Kieselguhr-Mullite (K-M) ceramic membrane substrate was fabricated by line compounding technique, where skeleton pores of Kieselguhr particles as the passage and dense Mullite as the linking substance. The substrate was proved by TGA, SEM, XRD, IR, mercury porsimetry and permeability measurement to be an ideal one with a narrow pore-size distribution of average pore-size 2.01 mum, porosity of 0.42 by volume and high permeability. There exist silica phase and Mullite phase stimulatingly, which demonstrates that it is successful in incorporating Mullite component by the precursor of silica-alumina sol. The front compressive strength of substrate is above 4.5 MPa and side one above 1.1 MPa when the content of Mullite phase exceeded to 10% (wt. %), which complete accorded to industrial applications.