Based on the mechanism of steady state continuous hydrocarbon expulsion of mature hydrocarbon source rock, the control of connected sandbody on oil-gas migration in terrestrial facies mature hydrocarbon source rock was analyzed, and the effects of contact area between hydrocarbon source rock and sandbody in it, content of sandstone in the bed series of hydrocarbon source rock with interbedded sandstone and mudstone, physical property, distribution and continuity of sandbody to expulsion efficiency of hydrocarbon were discussed. The results showed that the contact type between connected sandbody and hydrocarbon source rock was divided into vertical sedimentary facies transition contact, lateral sedimentary facies transition contact and staggered compound contact, and the vertical and lateral sedimentary facies transition contacts were the main types; the type for the combination of connected sandbody and hydrocarbon source rock was mainly steady state continuous hydrocarbon expulsion driven by abnormal pressure.