Abstract: The application of X-ray measuring technique in hot strip mill was analysed, combined with the RM312 profile gauge made by Thermo Radiometrie company in England. Various interference factors should be solved during the application of X-ray diameter measuring. The techniques of alloy compensation, temperature compensation, stereoscopic profile measurement and online standardization were introduced. The techniques eliminated the influence of interference. It provided ample real time measuring data for the strip profile control in hot strip mill.