In order to estimate the disk weight quickly and accurately and to grasp the development trend of the disk structure correctly at the conceptual design stage of new aircraft engines, the model based on equal strength profile and corresponding program for evaluation of disk size and weight is set up. A turbofan engine disk is estimated with the program mentioned above. It is studied that the disk size and weight change with the radius of the center bore and the value of AN2 of the rotor blade. In addition, it is also studied that the disk size and weight change with the replacement of the rotor blade material at different radius of center bore and different values of AN2. The results show that there exists an optimum combination of disk stress and the radius of the center bore to get the minimum disk weight under limits of strength load and structure. With the new material of lower density for blade, the radius of the center bore of the disk will increase so that the rotor structure becomes bling, its weight dropped significantly.