All forms of matter have the property of elasticity that can be compressed when the load increases and can spring when the load decreases, so do the porosity rock. The investigation of petroliferous basins over the world showed that one or more erosions had occurred after its reservoirs deposit which means unloading and leads to sandstone spring or interstice expanding so that the pressure fall in the reservoir underneath the erosion surface. The process could offer not only extra spaces for oil and gas accumulation but also the power to pump oil and gas. Based on geological analysis, a physical simulation experiment has been done, and the result of the experiment indicates that the lithology is the uppermost factor controlling the sandstone spring, and the confining pressure takes second place. And a mathematical model has been found between the sandstone spring process and the effective overburden pressure depending on the analysis of the experimental result. A comparison of sandstone-spring quantities between natural cores and artificial cores showed that the former is usually less than 1% and the last is usually more than 1%.