///According to the study on the thin section of well Fenggu 21 and well Chuanfeng 563 and the geology analysis, the authors think the main reservoir space of calc sandstone reservoir is the secondary solution pore and fissure owing to the solution process, which must belong to the fissure-pore type. The fluid which forms the calcite in pore and fissure is mainly resulted from the resolution carbonate rock detritus in the calcarenaceous sandstone.