Abstract: The Lamadian Oilfield is an asymmetric short axis anticlines reservoir with a gas cap under structural control, located at the north corner of the Daqing Placanticline. The Sa-0 reservoir occurs on the top of the Saertu oil layers, belonging to the 1st Member of the Nenjiang Formation of the Lower Cretaceous. Based on the cores, grain size, and well logging data, in combination with the sedimentary setting, three microfacies are well defined, e.i. subaqueous distributary channel microfacies; sheet-like sandbody microfucies and untabulated reservoirs. The main reservoirs consist of the distributary channel sands and sheet-like sandbodies. In this paper, we described the plane distribution of microfacies in sedimentary facies map, and revealed the tectonic characteristics and sedimentary environment while the Sa-0 reservoir was deposited. It was defined that the S-0 reservoir belongs to an external delta-front facies. The conclusion will help exploration in the region.