In order to reduce the engineering cost of muck improvement during the process of the excavation of Earth Pressure Balance (EPB) shield in composite stratum, based on the project of Guangzhou metro line 21 from Zhucun to Xiangling, the particle size distribution curve of composite stratum was calculated by particle analysis of different proportion combination residual soil of silty clay and gravel sand in this paper. Besides, combined with laboratory test and field test, the flow state and permeability of mixed residue soil were studied. The results show that when there is silty clay layer in the composite stratum, the flow state and permeability of the coarse-grained soil muck are greatly improved. Adding a small amount of bubbles or bentonite slurry, the muck state can meet the requirements of shield tunneling. When the content of silty clay is between 30% and 70%, the slag can reach a good plastic flow state. When the content of silty clay exceeds 70%, there is a risk of mud cake.