The marine facies shale of Lower Palaeozoic Erathem in the eastern Sichuan Basin is set of favorable shale gas reservoir. By means of observing field shale section and drill core, scanning electron microscope, analysising convention petrophysical property and micro-pore structure of shale, isothermal adsorption experiment, etc, we studied shale gas reservoir space characteristics in Lower Palaeozoic Erathem. The study shows that Lower Palaeozoic Erathem shale has 3 big kinds and 6 small kinds of pores and 2 big kinds and 5 small kinds of fractures. The shale gas reservoir has the characteristics of tiny and dense particles, few macropores and macrofractures, more micropores and microfractures, moderate porosity, low permeability, fine throat and bad connectivity. The total pore volume of shale is provided mainly by the micropores which are less than 200 nm. Nanoporous and microfractures are main shale reservoir space. To some extent, micropores in organic matter amplify the porosity of shale, and is the main micropore type in organic-rich shale. The storing status and flowing pattern of shale gas is very relevant with the micropores structure of shale. To some extent, the development degree of pores and fractures determines gas content and permeability of shale, but large or glant fractures would destroy effective preservation of shale gas. Micropores surfaces in organic matter(kerogen and asphaltene) and clay mineral are main spaces of storing absorbed shale gas, but organic matter supply most adsorptive specific surface, and is the main factor of determining shale adsorption property, and the effect of clay mineral is secondary.