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Three mian diagenetic processes, compaction, cementation and dissolution of Chang6 sandstone in Hu2 block of Huanjiang oilfield were identified and their impact on the tight reservoir quality were analyzed. Four pore types, intergranular, intragranular, moldic and micropores were identified. Porosity and permeability of low-energy facies with high level of muddy content were generally lower. A rapid loss of primary porosity was caused by compaction, proved by the abrupt change tendency at approximate depth of 2130m. Calcite was the dominant cement which plugged the intergranular pores, whereas other minerals like secondary overgrowth, kaolinite and illite also contributed to tightening the reservoir. [ABSTRACT FROM AUTHOR]