In order to improve the machining accuracy and measuring precision of bending angle, further research and optimization were done on the base of designed online measuring bending angle device and method, and a new measuring method was proposed. An online measurement system for measuring the angle of the elbow was composed of two online bending angle measuring devices by this method. The results show that the method eliminates influence by errors when a tube is installed in the bending machine on measuring of bending angle, which has improved angle measuring precision and the machining accuracy of bend.