Yuyuantan section of line 9 of Beijing Metro runs through waterrich largediameter boulder strata. The conventional stone crushing mechanisms and the mechanisms of stone crushing by shield machines are analyzed and the mechanism of stone crushing by means of sharp cutting and pressing is adopted for the project. The shield machine is optimized, proper shield boring parameters are selected, the shield boring management is improved and assistant technologies are used, so that the boulders can be crushed by the cutter head and cutting tools of the shield machine successfully. The progress rate and the wearing of the cutter head and cutting tools of the shield machine are analyzed and simulated, which demonstrates that ripper teeth have played an important role in the crushing of the boulders. Finally, suggestions are made on the optimization of the shield machine, including the optimization of the cutter head and the cutting tools.