The resistance line, as a core parameter in a blast design, is closely related to rock throwing distance and fragmentation degree, thereby directly affecting the fragmentation effectiveness and the final shape of the blast pile. Due to the significant complexity of an underwater blasting project, the factors affecting the effect of underwater blasting are intricate and complex, so it is essential to explore the impact of resistance line parameters on underwater bench blasting law through both drilling and blasting tests and numerical simulations using the FLUENT-EDEM coupling method. Four resistance line cases (2 cm, 4 cm, 5 cm, and 6.5 cm) were tested. The results indicate that as the resistance line parameter increases, the proportion of adequate energy used for rock fragmentation increases, resulting in a larger blasting funnel volume. However, with further increases in the resistance line, the explosive energy per unit volume of rock decreases, and the stress wave reflection intensity weakens. Consequently, the inhomogeneity of blasting block size first decreases and then increases with the resistance line. Additionally, numerical calculations effectively replicate the model test blasting effects, demonstrating that using the FLUENT-EDEM fluid-solid coupling method to study underwater bench blasting fragmentation is practical and feasible.