Abstract: In respect that the diameter of steel bar inside of concrete could not be measured effectively in traditional method, a new type of detection device based on pulsed eddy current array was proposed to detect both the thickness of concrete protective layer and the diameter of steel bar simultaneously. The detection model was simulated by ANSOFT simulation software, and physical experiments verified that the model had a good response to the thickness of the concrete protective layer and the diameter of the steel bar. Then, the BP neural network was used to establish the mathematical relationship of the coil signal to the thickness the protective layer and the diameter of the steel bar. The result of neural network experiment satisfied with the requirement basically. The new type of detection device could measure both the thickness of concrete protective layer and the diameter of steel bar at the same time, which the traditional eddy current detection equipment could not complete.