Abstract: Fixed dental prostheses with ceramic were widely used in people for their good strength and aesthetics. As the defect of the products will lead to failure in prostheses, good quality is essential in daily use. Accroding to analysis the date of the fixed dental prostheses in porosity test, and link with the shape and location of the pores, we have the result that the reject ratio of the fixed dental prostheses in porosity is exceed 40%, the main unqualified category is that big pores with diameter greater than 150 mm exist in ceramic. This may be introduced by the mechanic in the process of brush porcelain by mixing in bubbles or impurities.