Abstract: XAB Oilfield in Ordos Basin is located in Dingbian, Shaanxi Province. The main target layer is the shale interval in the seventh member of the Upper Triassic Yanchang Formation (Chang 7 member), with tight shale reservoir and high-angle fractures widely developed. Since 2011, rolling capacity construction and development by horizontal wells have been applied to produce the shale oil reservoir, which have the problem of low oil recovery degree and low production rate. In recent years, in order to research the high-efficiency shale oil development mode, tests of inter-well infill adjustment in horizontal well development zone have been conducted, and good results have been achieved in increasing oil production. Based on understanding of infill adjustment tests in the early stage, a “matrix-fracture” dual medium numerical model is established by fully considering the natural fracture features in the study area, and the infill adjustment parameters are optimized for horizontal well development zones with various production years, with the main parameters including infill timing, hydraulic fracture layout, horizontal well spacing and half-length of hydraulic fractures. A total of 76 infill adjustment schemes are designed to simulate and calculate the cumulative oil production of various schemed during the evaluation period. Furthermore, the financial net present value ratio is calculated and the economically beneficial schemes are ranked and optimally selected by using the financial cash flow method. The study results show that: (1) The longer the production period of the horizontal well development zone, the poorer results of infill wells. (2) The staggered layout pattern is better than the symmetrical layout pattern of hydraulic fractures. (3) The optimal infill adjustment parameters vary given the different infill timings. When the infill timing is 2-10 years, the optimal infill well spacing is 260 m, and the optimal half-length of the hydraulic fracture ranges in 140-180 m. On this basis, the horizontal infill adjustment design for Chang 7 member shale oil in horizontal well development zone in XBA Oilfield is conducted. After infill adjustment, the oil recovery factor and net present value ratio are expected to increase by 1.05% and 0.013 respectively, which supports to improve the shale oil development results and achieve good economic benefits.