Abstract: Jingbian gas field is a weathering crust gasfield,which is related to the Ordovician marine carbonate.Its distribution is strictly controlled by ancient landform.Located in southwest of Jingbian gas field,Shan181-400 well block is the key target of Jingbian gas field extension productivity construction in recent years.However,due to the lack of drilling data and unclear recognition of ancient landform characteristics in early stage,the progress of extension productivity construction has been restricted.Combined with the latest drilling data in recent years,the residual thickness method has been used to describe the Ordovician ancient landform and then the relationship between geomorphic unit and oilgas enrichment has been analyzed.Research results show:this area has 4 kinds of geomorphic units,namely denudation area,hill,slope and groove;its distribution pattern is western denudation area →middle slope →eastern hill;and the hill and slope are the potential productivity construction areas.The research achievements can directly guide the extension productivity construction,and provide reference for similar ancient landform areas.