Abstract: Based on the geological characteristics of shale oil reservoirs in Lucaogou Formation, Jimsar sag, this paper establishes a three-dimensional discrete element numerical model for the fracture propagation of dense cutting volume fracturing fractures, with a focus on well reconstruction. The model builds the randomly distributed natural beddings and high angle fractures according to the imaging logging data, as well as the sublayer and inter-layer interfaces according to the vertical layering data. It simulates the complex fracture propagation process under different cluster numbers and cluster spacing, analyzes the law of multi-fractures competitive propagation during the reconstruction by dense cutting volume fracturing, and the three-dimensional occurrence of the reconstructed fracture system. The numerical simulation analysis shows that:(1) During the dense cutting fracturing of shale oil reservoir, the degree of competitive propagation of multi hydraulic fractures increases with the increase of cluster number and the decrease of cluster spacing. (2) The competitive propagation of fractures is a dynamic balance process of in-situ stress, fracture morphology and fracture width. (3) The impact range of multi-fracture system is negatively correlated with the stimulated reservoir area (SRA) under the same pump displacement and fracturing duration. (4) High-angle natural fractures are easier to block and capture transverse fractures (main artificial fractures perpendicular to horizontal wellbore). (5) The enveloping area of the multi-fracture system is in the shape of a top hat, and the staggered arrangement of the fracturing sections of adjacent wells is helpful for reducing the seepage distance of oil and gas in the undeveloped reservoirs