Pile-side grouting is the main method to enhance the bearing capacity of in-service pile foundation, the formation parameters have complicated influence on the grouting reinforcement effect. For the problem of inadequate bearing capacity of friction piles in service in alluvial river plains, the effect of the parameters of the complex strata of silty clay and fine sand on the bearing capacity of friction piles reinforced by extrusion grouting was investigated by model tests. When the thickness ratio of powdered clay and fine sand stratum changes from 1:3 to 3:1, the proportion of powdered clay in the stratum increases, and the bearing capacity of the pile foundation decreases by about 50∼100 N. The internal friction angle of fine sand is larger with the particle size increase, and the load transfer efficiency is higher, so the effect of pile side compaction grouting reinforcement is more pronounced. Meanwhile, the water content of powdered clay plays a negative role in the impact of pile foundation grouting reinforcement.