Abstract: Based on the Longtan Formation shale in the northwestern Guizhou, the shale reservoir characteristics of Longtan Formation in the northwestern Guizhou were studied based on organic geochemistry, mineral composition, FE-SEM, specific surface and pore size, N2 desorption and isothermal adsorption etc. The results show that the shale of Longtan Formation in northwestern Guizhou has a high abundance of organic matter and a Type III Kerogen,which is in an over mature stage and has good hydrocarbon generation conditions. These shale samples mineral composition is mainly clay minerals and quartz, of which clay mineral compositions have the highest content of illite and Illonite/Montmor mixed layer; The brittleness index is 57.6%, indicating that the shale of Longtan Formation has good brittleness with low porosity, various pore types, and pore size is mainly mesopore; The N2 adsorption-desorption curve shows that the fractal dimensionD1 of Longtan Formation shale samples is 2.68～2.77(relative pressure≤0.5),D2 is 2.70～2.89(relative pressure>0.5). The values ofD1 andD2 are large, reflecting that the Longtan Formation shale has a heterogeneous pore heterogeneity and a complex structure. The fractal dimensionD1 andD2 have a good positive correlation with the specific surface area and a good negative correlation with the average pore size of the shale.