No. 1 Line and Phase I Project of No. 2 Line of Chengdu Metro are constructed by foreign shields. These foreign shields, which are difficult to be optimized, cannot be well adapted to the actual conditions of the project. Therefore, CREC shields are designed on basis of the complex geological conditions in Chengdu, especially the waterrich sandcobble strata. In the paper, study is made on the optimized design of CREC shields in terms of main drive, cutter head design, opening ratio, ground conditioning and screw conveyor. The comparison and contrast between foreign shields and CREC shields shows that CREC shields have good adaptability, reliability and efficiency and can achieve continuous longdistance boring in fullface waterrich sandcobble strata.