In order to realize the intelligent detection，accurate perception and identification of coating defects on the outer surface of steel box girders in a special complexenvironment，we developed the robot technology，multi-dimensional in-situ non-destructive inspection and defects identification software integration. In this work，a magnetic adsorption wall-climbing robot technology was studied，the portable inspection equipment such as high-definition camera modules，hyper-spectrometers，and X-ray diffraction detector were developed，and an expert decision-making system for image recognition of steel structuresurface defects was built. It realized an intelligent detection technology for steel structures surface coating defects. The results showed that，in the actual bridge test of the Hong Kong-Zhuhai-Macao Bridge，this technology achieved a surface inspection coverage of 91. 25% of key facilities，an intelligent identification rate of typical defects of 90. 3%，a positioning accuracy of 7 mm，and the ability to identify linear defects with a width of ≥0. 104 mm. Thepatchy defect area was ≥0. 93 mm×1. 02 mm，which met the urgent need for efficient，accurate and safe inspection of the outer surface of the steel box girder for the bridge.