Cement concrete is a composite material employed in a multitude of engineering construction projects. The setting state of cement concrete exerts a profound influence on the advancement and security of such endeavours. It has been demonstrated that the setting time of cement concrete is contingent upon the water content. Therefore, a water content sensor based on the principle of capacitance detection is designed to measure the water content of cement concrete. According to the dielectric properties of cement concrete and the detection principle of capacitive sensors, and utilising the edge electric field to extend the measuring range, capacitive edge electric field sensors of parallel plate and cylindrical types were designed. A finite element simulation analysis was conducted using COMSOL software, and the cylindrical structure was selected based on a comparison of the penetration depth, sensitivity and signal strength of the two sensor structures. Subsequently, the performance of the cylindrical sensors with different parameter combinations was compared by orthogonal experiments, and the optimal parameter combinations of the sensors were determined as electrode spacing of 5 mm, electrode width of 50 mm, and electrode radius of 15 mm. This configuration enabled the sensors to reach a depth of penetration of 66.86 mm, a signal strength of 11.387 pF, and a sensitivity of 0.267. Finally, the developed sensor was utilised for the actual measurement of cement concrete with varying water contents, and the output capacitance value exhibited a satisfactory linear relationship with the water content, with a non-linear error of ±1.276% and a maximum relative error of 1.533% in comparison with that of the weighing method, which demonstrated a satisfactory measurement effect.