This paper briefly clarifies the basic geological theories of vitrite refle-ctivity（R

o

max）and gives a preliminary discussion with R

o

max on the con-ditions of oil and gas origin in Taiyuan formation of Carboniferous Sys-tem in northern Ordos Basin.It is suggested that R

o

max ranging from 0.5to 1.3% is confirmed as the main stage of oil formation;0.5%

as im-mature stage;1.3%

as overmature stage

that is

gas formation stage.The result shows that the organic matter of Otoc County and its south ernregion have reached overmature stage;in its northern region

the Taiyuan formation is just at the main mature stage

but the conditions of conser-vation on both sides of east and west are rather defective

the availableregion is only restricted in a narrow zone in the southern part of the west.Finally

in combination with the geotectonic evolution

sedimentary cha-racteristics and lithofacies of the basin

the districts of oil and gas pot-ential

of Taiyuan formation has been divided.