In order to improve the working efficiency of special equipment testing workers to measure the flexible value under the main beam of the crane, ensure the measurement accuracy and realize the intelligent processing of measurement data, a measurement method based on horizontal laser and photoelectric sensor is proposed, and the principle prototype of the measuring system is designed. The measuring system transforms the arch value of the crane into the height difference of horizontal laser irradiation on the photoelectric sensor array and improves the measurement resolution by the arrangement of the horizontal beam; ensures the horizontal illumination by the focus instead of the horizontal laser in the result with the function of LoRa and 5G wireless communication technology. In the field of a crane girder detection, the system prototype designed in this paper and the traditional theodolite method contrast measurement experiment, the results show that the measurement method and this paper designed the system prototype compared with the traditional theodolite method, the measurement error of each point are less than 0.6 mm, in the experiment, and the total measurement time reduced by about 70%, ensure the measurement accuracy and reliability, significantly improve the measurement efficiency, implements the measurement data real-time upload to the cloud, improve the intelligent degree of the detection work.