For the problem that the detection accuracy of the concrete coating thickness in port and waterway engineering by the microscope and ultrasonic dry-film thickness gages cannot meet the accuracy requirements of relevant standards，we investigate the accuracy requirements of ultrasonic coating thickness gauge in relevant specifications at home and abroad，select two accuracy requirements of ±2 μm and ±5%，measure the thickness of standard samples with the actual thickness of 53 μm，129 μm，252 μm，492 μm and 2 349 μm，and analyze the relationship between measurement deviation and accuracy requirements. The results show that the accuracy of ± 5% is more suitable for the thickness detection of concrete coating in port and waterway engineering.