In order to improve the desulfurization efficiency of the SDA semi-dry system, the SDA-powder spraying desulfurization test system is built, and semi-industrial experimental research on the influence of powder spraying on the desulfurization efficiency of the system is launched. The results show that the influence of powder spraying position on the desulfurization efficiency is significant, with the decrease of powder spraying position, the desulfurization efficiency gradually decreases, and the best position of powder spraying is located in the upper area of the tower, and the desulfurization efficiency can reach 75.90%, which is 19.10% higher than before powder spraying. With the increase of powder spraying, the desulfurization efficiency increases, and the desulfurization efficiency increases from 57.90% to 87.20%, but when the powder spraying amount is too high, the effective utilization rate of desulfurization ash decreases compared with before, and the desulfurization efficiency tends to be flattened. The appropriate amount of humidification water can effectively improve the utilization efficiency of desulfurization ash, and for the spraying amount of different desulfurization ash, the appropriate humidification water ratio should be carried out to achieve the best desulfurization efficiency.