Abstract: To increase the drilling success ratio in reservoirs of horizontal well in S190 well block,the low amplitude folds of top surface of Ma513 that was the main gas layer in Ordovician were drew,after applying some ways including make synthetic seismic record,horizon demarcate,the combination of the structural trend surface of horizon demarcate(Tc and T014) with the thickness ratio of formation classification of every well and lateral prediction based on the 3d- seismic explanation and logging and drilling data.Moreover,the thickness between the bottom of Carboniferous and the bottom of Ma522 and the Ordovician paleokarst landform were mapped by way of the strata thickness and the impression method.Then,three maps above were analyzed comprehensively,the relationship between both horizontal well trajectory that were drilled and the top surface of Ma513 were basically matched as related coefficient 0.6548 and 0.8547.Thus,this paper gives rise to highly important guiding and practical significances on the horizontal well deployment site and search high productivity zones of gas field,where the higher position of the paleokarst landform,the thicker place of reservoir and the higher location of present structure map were coincident.