Mercury injection capillary pressure (MICP) experiment is one of the most important methods to study the pore structure of reservoirs, which can reflect the complete pore throat distribution of reservoirs. In this paper, a systematic method of fitting, characteristic parameter extraction, upscaling and automatic classification of the capillary pressure curve is proposed. By improving the conventional single hyperbolic tangent function model, a new multi-hyperbolic tangent function is established to fit MICP curves; on this basis, an upscaling model with the volume ratio of rock components as the weighting coefficient and a classification method based on the comparison of the curve’s complete morphology are established, which realizes a systematic and quantitative analysis of the MICP curves of complex rocks. The multi-hyperbolic tangent function model can accurately fit any complex MICP curves, and automatically extract the number of sub-pore systems, maximum pore throat radius, effective pore throat radius, selectivity and other characteristic parameters of each sub-pore system; the characteristic pore structure parameters of the whole pore system can also be calculated. The volumetric ratio of rock components obtained from core observations or digital image analysis are used as the weighting factor for upscaling MICP curves, which effectively solves the problem of representativeness of MICP curve in strongly heterogeneous reservoirs. Based on point-by-point mercury saturation comparison, the allowable error range is adjusted, which effectively solves the defects of classification method based on single characteristic parameter that is prone to classify curves with large morphology differences into the same group. The proposed method can achieve quantitative and accurate characterization of MICP curve of any complex morphology, overcome the defects of the traditional Thomeer formula and Gaussian model, and provide an important reference for the classification of rock types, as well as improve the reliability of reservoir evaluation and pore structure study.