Abstract: Mini-frac test analysis is one effective measure to clarify reservoir characteristics, optimize main fracturing design and improve construction efficiency. In this paper, the mini-frac test results of 20 wells in the Nantun Formation of Hailaer Oilfield were analyzed using FracproPT2011 fracturing software. Then, combined with the development characteristics of reservoir faults and the triaxial test results of rock mechanics, the objective causes of the difficult fracturing operation in field were researched. It is indicated that the bottom hole pump-off pressure gradient and closure stress gradient for fracturing the reservoir of Nantun Formation are 0.018 0−0.026 9 MPa/m and 0.015 4−0.023 2 MPa/m, respectively, averaging 0.021 6 MPa/m and 0.019 4 MPa/m. The gas test permeability is mainly in the range of (0.1−0.3)×10⁻³ μm², accounting for 65%, and there are natural fractures and hydraulic multi-fractures. The perforation friction and near-well tortuosity friction in the process of fracturing are in the range of 0.85−2.86 MPa and 1.42−14.36 MPa, respectively. The principal tectonic stress induced by developed faults is in the range of 5.0−10 MPa, the minimum horizontal principal stress gradient is 0.016 4 MPa/m, and the Young’s modulus and Poisson’s ration of rocks are 36 090−38 400 MPa and 0.24−0.39, respectively. And additional tectonic stress, higher minimum principal stress, high Young’s modulus and high Poisson’s ratio are four main reasons for the abnormally high construction pressure and pump-off pressure, low proppant concentration and easy sand blockage during the fracturing of the reservoir of Nantun Formation.