When large diameter slurry shield machines are used for long distance boring in complex sandcobble strata, the cutter heads and the cutting tools are often seriously worn, the slurry feeding/discharging pipes are often seriously damaged, the stone crushers and the slurry gates often have malfunctions and other incidents often occur, therefore, the shield machines often have to stop boring, which reduces the performance of the shield machines and even jeopardizes the construction safety. Optimizations are made on the cutter head and cutting tools, slurry cycling system, stone crusher and slurry gate, electrical system and monitoring system of a 12mdiameter slurry shield used in Beijing, so as to optimize the design of the shield machine, facilitate the inspection and repair of the machine and minimize the construction risks. In the end, the availability and working efficiency of the shield machine are improved, the construction risk and cost are reduced and the safety of the labors and the equipment is guaranteed.