Abstract: To solve the problem of steel strip detaching off as occurring during the production process of the spiral welded pipe that is not detected and corrected timely，and consequently causes such abnormal states of the steel strip as off-milling，over milling，uplift and distortion，and to improve the formation quality of the steel strip，a measurement and warning system for steel strip width and position is developed. The system as equipped with three sets of high-precision grating rulers is capable of real-time detecting the width and position of the steel strip at different positions in the forward direction. And the detection results are collected into the Siemens PLC300 for processing and threshold comparison. Then the comparison results are output to the MCGS screen，so as to produce alert through indicator lights and horns. The actual testing result demonstrates that measurement error accuracy of the said system is within 1 mm，so that it is satisfactory to the manufacturing process requirement，and ensures consistent work width and deviation within the permissible error margin of the steel strip，which provides a necessary assurance of consistent formation of the pipe with the steel strip.