In order to understand the stress changes of various points in sandy frozen soil, tension-compression conversion, fissure development on the surface, the rupture process, the expansion speed and scope of frozen soil duing blasting, the dynamic characteristics of thin-layered sandy frozen soil were analyzed in this paper. The blasting process of frozen soil is regarded as a dynamic pressure operation process of gas expansion chamber under thin plate. The gas pressure in blasting chamber obtained by adiabatic gas state equation is approximate close to the actual expansion pressure. At the same time, a moment of frozen soil blasting process is regarded as a model that a peripherally-fixed solid circular plate is suffered to a concentrated force in the center of circle. Through calculation and blasting funnel tests we can see that the frozen soil is suffered to much smaller force along horizontal direction than normal direction. Along with the time and expansion of blasting chamber, pressure of frozen soil is quickly reduced. And it is discovered that regardless of any stage of explosive, there appears the critical point of changes from tension to compression along the direction from explosive center to the all-around within a radius of about 0.9 m. This model can provide a theoretical guidance for the analysis of dynamic stress and the selection of blasting parameters for frozen soil blasting.