Cementation in sandstone is very important retention processes in reservoir evolution , which enables porosity in deepburied sandstones to preserve. Based on the studies of occurrences of dolomite (ankerite) cement , quartz cement and clay cement and the timing and mechanism of cementation from Paleogene sandstone of East China Sea Basin , Upper Paleozoic and Triassic sandstone of Ordos Basin and Triassic sandstone of Sichuan Basin , a suggestion that large part of cementations occur at the early stage of diagenesis before effective compaction is presented here. Some of these cementations are related to tectonic uplift during earlier burial , and some to early acid fluid in coalbed. Partial and early cementation could enhance the mechanical strength of rocks and the resistance to porosity loss with depth and compaction by change of the porosity depth curve during shallow to deepburial diagenesis , which takes a significant part in reservoir quality prediction.