Abstract: Fuzzy system method is applied to concrete undamaged inspection. In the model, the inputs are rebound value, ultrasonic value, carbonation depth value and moisture rate. The output is the compressive strength. By the sample data training, fuzzy rules can be extracted. All rules constructed a complete base of fuzzy IF-THEN rules. Using the singleton fuzzifier, the product inference engine, and the center-average defuzzifier, the fuzzy system model of concrete undamaged inspection is obtained. The experiment shows the average relative error of the predicted results is 7.89%, and the relative standard error is 10.53%. The prediction accuracy of the fuzzy model is obviously higher than that of the regression model. A method is further proposed to rank the importance of the input variables. The result we obtained shows that the rank is: rebound value, ultrasonic value, carbonation depth value, and moisture rate, with rebound value being the most important. It can help us to select the more important ones as the inputs to the model so as to achieve the efficiency optimization of the model.