To solve the problem that the dry film thickness of the concrete coatings was difficult to be tested nondestructively, ultrasonic coating thickness gauge was adopted to measure the dry film thickness of coating on the surface of concrete in different strength grades. Uncertainty evaluation and quality judgment of the measurement results were conducted. The results show that the degree of reliability of the measurement results could be found by the uncertainty evaluation, which is the important basis for quality judgment whether the measurement result satisfies the requirements or not. The higher the strength grade of concrete is, the smaller the uncertainty of the dry film thickness of concrete coatings is, and vice versa.