Abstract: According to sedimentology theory and sequence stratigraphy, favorable environment and time for dark organic shale was analyzed and we consider favorable condition for gas system and take domestic and foreign examples in the progress. It can be concluded that dark organic shale, commonly developed in transgressive system tract, especially in condensed section. Arm of lake, semi-deep and deep lacustrine in continental sedimentary basin, and semi-deep and deep sea basin, platform margin deep slope and blocking gulf in marine sedimentary basin are appropriate places for dark organic shale developing. Depending on the analyses of Barnett shale gas system in American, we could say that contour map of TOC, Ro and isobaths of dark mudstone, and so on, are important basic geological maps, and using these maps for shale gas exploration will be an excellent method.