Abstract: Based on the present situation of hard to judge the sedimentary hiatal surface in ultra thick seam, in order to more accurately and reliably judge the sedimentary hiatal surface in ultra thick seam, taking the No.4 ultra thick coal seam in Yan'an Formation of Binchang Coalfield of Ordos Basin as an example, the logging data analysis, coal petrography and coal quality analysis, stable carbon isotope analysis of organic matter, 1D continuous wavelet transformation as well as Milankovitch Cycle discriminate were applied to make a study on the comprehensive distinguishment of the sedimentary hiatal surface in ultra thick seam and the control factors of the cross section development. A set of methods to quantitatively distinguish the sedimentary hiatal surface in the ultra thick seam was provided. Research results showed that, the hiatal surfaces identified by different discriminant methods were assignment, weighted and scoring, the control factor of the hiatal surfaces was eccentricity, found out by Milankovitch Cycles, which could make the discriminant results of the hiatal surfaces in ultra thick coal seam more quantitative and more reliability.On those circumstances, a genetic mode of the sedimentaryhiatal surface in ultra thick seam in onshore zone was preliminarily summarized.