By the comprehensive analyse grain size analysis, thin slices, pore image, SEM, mercury-injection data, the pore and pore-throat sizes distributions in two low permeability sandstone reservoirs with different origins, E1f3 in Shanian area, Subei basin, and J2x in Niujuanhu area, Santanghu basin, are analysed. The different origins of them is studied. The research shows, the pore types is mainly carbonate cement and feldspar dissolved pores in E1f3, tuffaceous and feldspar dissolved pores in J2x. There are more and greater dissolved pores, less intercrystal pores in E1f3 than in J2x. The pore-throat size distributions in E1f3 are gross single-peaked curve with dissolution origin pore-throats, fine single-peaked curve with compaction or compaction- cementation origins pore-throats, double-peaked curve with dissolution origin pore-throats and compaction or compaction- cementation origins pore-throats, and peakless curve with tube bundle pore-throats. The pore-throat size distributions in J2x are are gross single-peaked curve with dissolution origin pore-throats, small single-peaked curve with tube bundle pore-throats, and double-peaked curve with tube bundle pore-throats and compaction or compaction- cementation origins pore-throats. The pore and pore-throat sizes decrease with the grain size being smaller, and the pore radius is always smaller than size. The higher maturity and early phase carbonatite cementation make the E1f3 keeping larger primary origin intergranular pore-space, which are enlarged by dissolution. The higher plastic detritus content and consedimental tuffaceous make origin intergranular pore-space of J2x decreasing greatly, and the latter dissolution is feeble. They are the main orgins of the pore structures difference of two sandstone reservoirs.