Abstract: Exemplified by the Leng-94 well in the Lengjia district, Liaohe Basin, the diagenetic history, diagenetic sequences and porosity evolution and trends are examined on the basis of thin-section, SEMP, energy spectrum and cathodoluminescence examination. The diagenetic stages may be divided into:(1) syndiagenesis; (2) early stage of early diagenesis; (3) late stage of early diagenesis, and (4) early stage of late diagenesis. The porosity evolution has been explored here in the aspects such as compaction, coatings of clay minerals, cementation of calcite and dolomite, solution of feldspar, secondary overgrowth of quartz and precipitation of microcrystalline quartz.