Abstract: The design of filter function is very important in the CT reconstruction.In order to improve the image quality,a new method of filter function design was presented based on the FBP theory.Based on the simulated data of Shepp-Logan and the projection data of conch,the compared result of CT reconstruction using R-L filter function,S-L filter function and a new filter function based on the new design method was given.The reconstruction result of the new design filter function was the best in overall performance.In local areas,the density resolution had increased.So this paper provided a novel method for filter function designing in CT reconstruction.