Abstract: With the increasing exploration in mature areas and main layers in Yinggehai Basin, new layers in new area gradually become the focus of attention increasingly. Yingbei District is located in the northern part of Yinggehai Basin, and the First Member of Sanya Formation as the target layer has great exploration potential, but the exploration degree is low at present and the sedimentary system and reservoir development are lack of systematic research. Through drill core observation, microscopic thin section identification, seismic data, well logging data, and laboratory analytical data, the sedimentary facies and distribution characteristics, reservoir characteristics, diagenesis and other aspects of the target layer in the study area were studied, and the controlling factors of reservoir development were discussed. Results show that: ①The First Member of Sanya Formation in the HK29 area develops mainly proximal delta sediments influenced by the provenance in Hainan Island. The submarine distributary channel microfacies is a favorable facies belt; ②The lithology of the reservoir rocks in the First Member of Sanya Formation is mainly feldspar lithic sandstone and lithic feldspar sandstone, the pore types are mainly feldspar-dissolved pores and inter-granular pores, and the overall performance is characterized by medium-low porosity, low permeability to ultra-low permeability; ③The sand bodies in the underwater distributary channel at the delta front are coarse-grained and well-sorted, which is an advantageous facies belt for the development of favorable reservoirs. Compaction is the direct factor for the deterioration of reservoir properties in this area. The dissolution of feldspar and rock fragments is the key factor in improving reservoir properties. The reservoir physical properties are mainly controlled by sedimentation and diagenesis. The sandstones in the submarine distributary channel in the delta front are coarse-grained size and well-sorted, which is the advantageous facies for the development of favorable reservoirs. Compaction is the direct factor for the deterioration of the reservoir physical properties, and the dissolution of feldspar and lithic is the key factor for improving the reservoir physical properties. Base on the above research, the formation mechanism of the high-quality reservoir in the First Member of Sanya Formation in the HK29 Area with “excellent facies belts, shallow burial, and strong dissolution” was proposed, which effectively guided the exploration breakthrough in Yingbei District.