Abstract: In response to the challenges in evaluating the performance of decomposition agents in the treatment of muck cakes in shield air bubble chamber, and the difficulty in accurately determining the optimal agent parameters,this study, based on a shield tunnel project, developed a muck cake compaction device and a decomposition effect evaluation device. Muck cake specimens were fabricated by compacting muck cake-prone formation soils using the compaction device, and their decomposition behavior under different types and concentrations of decomposition agents was investigated. The optimal decomposition agent was identified and subsequently applied in the shield air bubble chamber treatment. The results indicate that: (1) The decomposition process of muck cakes in water can be divided into three stages: initial water absorption, rapid decomposition, and stabilization. In the initial stage, muck cakes first absorb water and then start decomposing; during the rapid decomposition stage, the decomposition rate is high and decomposition mass increases rapidly; in the stabilization stage, the decomposition mass no longer significantly increases. (2) The best decomposition performance for muck cake specimens was achieved using decomposition agent A with 6% concentraion. (3) After injecting the decomposition agent solution into the shield chamber, the muck cake on the cutterhead was effectively removed, resulting in noticeable reductions in shield thrust and cutterhead torque, as well as a significant increase in advance rate, confirming the excellent practical effectiveness of the selected decomposition agent in muck cake treatment.