Abstract: To improve the low energy efficiency and poor half-hole retention associated with smooth blasting in small-section hard rock roadways within metal mines, this study established numerical models using LS−DYNA to simulate blasting with both water-decoupled and air-decoupled charging. The effects of different coupling media, peripheral hole spacing, smooth blasting layer thickness, and in-situ stress on smooth blasting performance were systematically investigated. The results show that, under the same decoupling coefficient, water-medium decoupled charging exhibits significantly higher borehole wall peak pressure and circumferential tensile stress and a significantly larger rock mass damage area than air-medium decoupled charging, with better inter-hole crack coalescence. As peripheral hole spacing increases, the stress wave superposition effect weakens, and crack coalescence becomes more difficult. Air-medium charging fails to form through-going cracks when hole spacing exceeds 80 cm, while water-medium charging can still achieve crack coalescence at 100 cm spacing. In-situ stress significantly influences the direction of crack propagation, with cracks tending to propagate along the direction of the maximum principal stress. Considering both smooth blasting layer damage and inter-hole crack formation quality, a parameter combination of 80 cm peripheral hole spacing and 50 cm smooth blasting layer thickness with water-medium decoupled charging is recommended. The research results can provide a theoretical basis for optimizing smooth blasting parameters in hard rock roadways.