Liquid-nitrogen-based Artificial Ground Freezing (AGF) is widely used in underground engineering because of its rapid cooling capacity. However, axial temperature non-uniformity along freezing pipes remains a key challenge, as it directly influences freezing-front development and overall thermal efficiency. This non-uniform behavior is primarily governed by the strong coupling among multiphase flow, jet impingement, phase transition, and conjugate heat transfer within perforated inner pipes. In this study, an indoor liquid-nitrogen ground freezing experimental system was established, and laboratory tests were performed using a uniformly perforated inlet pipe. A two-dimensional numerical model consistent with the experimental conditions was subsequently developed and validated to simulate the coupled multiphase flow and phase-change heat transfer processes. The research primarily focused on elucidating the influence of perforation configuration on the longitudinal cooling characteristics of the freezing pipe. The results show that rapid phase transition after injection induces intense heat absorption and a sharp decline in pipe-wall temperature, resulting in a pronounced longitudinal temperature variation along the pipe. Parametric analyses reveal significant nonlinear effects of spacing and diameter. Excessively small spacing causes premature upper cooling and insufficient lower cooling, whereas overly large spacing induces periodic temperature fluctuations. Similarly, small diameters concentrate cooling locally, while large diameters may reduce overall heat transfer efficiency. An optimized perforation configuration improves axial temperature uniformity and freezing performance.