Belonging to the field of porous 
ceramic materials, the invention in particular relates to a pure foam 
silicon carbide support membrane tube with a three-gradient pore structure and a preparation method thereof. According to the foam 
silicon carbide support membrane tube, a dual-gradient pore structure pure foam 
silicon carbide support and a 
surface film layer form a three-gradient 
filtration structure, the support is composed of a dual-gradient pore structure pure foam 
silicon carbide support, the average pore size of the outer layer is 300-500micrometers, the average pore size of the inner layer is 1-3mm, and the support 
porosity is 35-65%; the 
surface film layer is formed by combination of 
silicon carbide powder, the pore size is 50nm-20micrometers, and the film layer 
porosity is 35%-50%. The preparation method comprises the following steps in order: burdening, foam support molding, support 
sintering, film layer preparation and firing. The pure foam 
silicon carbide support membrane tube provided by the invention can be used in oxidizing 
atmosphere and 
reducing atmosphere, has strong acid and alkali 
corrosion resistance, and can be used for 
coal gasification 
chemical engineering and IGCC, PFBC 
coal gasification power generation, high temperature 
flue gas, automobile exhaust, water purification and other high and low temperature 
fluid filtration purification.