The work aims to optimize the design of ammunition packaging size, so as to improve the efficiency of loading and transportation of ultra-long ammunition packaging. With the skewed transportation of ultra-long ammunition packaging by railway as the research object, the mathematical relationship between the geometric size of ammunition packaging container and carriage was analyzed, so as to construct a mathematical model of the maximum length, minimum length and maximum width of ammunition packaging allowed by carriage changing with the skewed angle during skewed transportation. Based on this model, the parameters of packaging container were optimized to realize the maximum loading capacity of railway carriage. With a certain carriage as the example, MATLAB was used to analyze the established model. The change law of ammunition packaging parameters with skewed installation angle under the condition of a given carriage size was obtained. The established mathematical model can be used to determine the size series of ammunition packaging suitable for skewed transportation by railway carriage, which provides a theoretical basis for the optimal design of ammunition packaging and efficient loading and transportation.