The detector optimization is a critical task in the design of the CEPC detector to ensure that the physics goals of the CEPC project will be achieved. On one hand, in order to make the best use of all Higgs bosons generated at CEPC, the detector design should consider high-efficiency reconstruction and precision measurement of all the physics objects including leptons and jets, and of other key spatial and kinematic variables including the displaced vertices, charged track trajectories, missing energy and momentum of jets. . On the other hand, the cost and the operation of the detector , such as power consuming and active cooling, should also be taken into account. Starting from a baseline that follows the ILD detector design, a series of detector optimization studies have been performed. This report will summarize the progresses and results.