The mechanical compaction is generally regarded as a main diagenesis of sandstones in shallow layers. And it is ignored in deep strata for a long time. In recent years, the genetic mechanism research of the tight sandstones has been a central issue. In order to resolve the problem this paper utilizes porosity contrast between shallow layers and deep layers, microscopic view of sandstones composition and simulated experiment of sandstones compaction to analyze the features of the compaction. The research has found that the trend of pore decreasing between shallow strata and deep strata is consistent or parallel. And as the addition of overburden pressure, the porosity of sandstone has been decreasing and the compaction becomes stronger with the depth gets deeper. In addition, the samples data of microscopic view are all in the lower left area of the evolution map that the compaction and cementation affect the porosity. The results demonstrate that the compaction is always exists in the burial process of sandstones. It is a vital factor to densification of sandstones and its effect of pore decreasing is far greater than the action of cementation. Because the mathematical derivation of porosity evolution indicates that the compaction is controlled by burial depth and burial time, so the pore deceasing amount can be analyzed quantitatively by the binary function and then the affect degree of the compaction to the process of sandstones densification can be gained.