<p>A CFD simulation was conducted in a bottom lead smelting furnace to reveal the complex flow within the air-slag-lead system. The results demonstrated that variations in tuyere angle significantly influence molten bath agitation intensity by governing the gas flow trajectory and recirculation patterns within the bottom blown lead smelting furnaces. Specifically, a critical tuyere angle was found, beyond which the melt splashing not only reaches the top wall of the furnace but also moves downward along the furnace side wall, thereby generating strong backflow that stirs up the bottom lead layer. This stirring effect causes the gas inlet to directly expose to the slag layer, which has much lower density than that of the replaced lead layer, resulting in dramatic changes in bath agitation. Correspondingly, onsite observations of the furnace under conditions corresponding to the simulated cases revealed excessive metal loss and lining impact, confirming the existence of unexpected agitation in practice. Therefore, the tuyere angle for lead smelting furnaces is suggested to be maintained below the critical angle to avoid excessive damage to furnace lining and extra loss of valuable metals. Moreover, in the tuyere angle range below the critical value, periodic axial migration of low velocity regions was observed along the furnace body, effectively contributing to the elimination of dead zones in the bath.</p>