Spur dikes are one of the commonly used waterway regulation structures，and scattered riprap spur dikes are especially popular in actual projects. This type of spur dike has a certain degree of water permeability，and different porosity has different effects on improving the water level near the permeable spur dike. Resorting to the computational fluid dynamics software FLOW-3D，this paper studies the influence of porosity on the water level changes at different parts of a permeable spur dike，including its body，the front of its head，and its main flow area. The results show that the variations of water level with porosity at those parts are similar. In the upstream section of the spur dike，the water level first decreases and then rises as porosity increases when the latter is lower than 15.4%. When the porosity is higher than 15.4%，it decreases to a certain value and then stabilizes. At the axis of the dike body，the water level fluctuates up and down with increasing porosity. The water level behind each permeable spur dike is higher than that in the case of solid spur dikes. Nevertheless，water levels behind the dikes are not positively correlated with porosity.