Pitting corrosion on the bottom plates of storage tanks is the primary cause of failure, and the three-dimensional morphology of pits is the crucial data for corrosion evaluation. Existing statistical studies on pitting corrosion mainly focus on one-dimensional or two-dimensional parameters, such as depth and aspect ratio, without fully reflecting the three-dimensional morphology of pits. To elucidate the evolution of the three-dimensional morphology of pitting under the oil-water-sludge covering layer on storage tank bottom plates, corrosion tests are conducted using Q235 steel. Surface morphology testing methods and MATLAB software are employed to statistically analyze the morphology and evolution of corrosion pits on the carbon steel surface. A classification method for pit types based on morphology is proposed, and mathematical representations of the three-dimensional morphology of different pit categories are developed. Furthermore, the evolution of pit morphology is characterized using typical parameters from mathematical functions. Corrosion pits are categorized into parabolic, conical, bimodal and flat-bottomed. The results show that during different corrosion stages, the shapes of the pits are mainly parabolic and conical. Parameters representing horizontal dimensions and surface inclination of pits follow a log-normal distribution, with the logarithmic mean (μ) showing an inflection point at 60 days of corrosion. Pit depth parameters follow a Gaussian distribution, with the mean value (μ) exhibiting an exponential increase with corrosion time.