Abstract: The law of slurry flow has significant influence on the parameter design and technical effect of isolated grouting. The slurry flow is controlled by the grouting pressure,and the actual grouting pressure consists of zero pressure,supercharging and other stages. The study shows that the injection-production ratio in the non-pressure stage can reach up to 10%,and the study of the slurry diffusion law in this stage is helpful to optimize the slurry parameters and borehole layout at the initial stage of grouting. For this reason,this paper adopted the theoretical analysis and experimental research methods to carry out the research on the diffusion law of overburden isolated grouting filling grout in the stage of no pressure grouting. The dimensionless formula of slurry diffusion distance was established by dimensional analysis.A visualized slurry diffusion simulation system was designed,and the experimental study of slurry diffusion law was carried out. The experimental system consists of transparent plexiglass plate,visual simulation of cracks,constant rate grouting pump,mixer and monitoring. The influence of grouting flow,end hole distance and crack height,slurry viscosity on slurry diffusion distance and slurry morphology was studied by using this system. The experimental results show that the diffusion of slurry has gone through two stages:radial diffusion and bidirectional diffusion. Among them,the radial stage presents a circular diffusion centered on the grouting hole,and the two-way stage presents a symmetrical planar diffusion on both sides. Based on the experimental results,the diffusion distance formula of the slurry in the non-pressure phase was solved,and the validity was verified. At the same time,the simplified description model of slurry morphology in two stages was obtained,and the calculation formulas of slurry thickness at different diffusion times and locations were derived to clarify the slurry diffusion law in the non-pressure grouting stage. Based on the research results,some suggestions were put forward for the grouting filling design of isolated overburden grouting filling in the no-pressure stage.