The invention relates to pipe machining auxiliary equipment and in particular to a real-time measurement device for measuring the outer diameter of a steel pipe. The measurement device consists of an adjusting part, a measuring part and a data display part. The measurement device is compacted on the outer wall of the steel pipe through a support wheel under the action of a back pressure spring, so as to reflect the change in outer diameter of the steel pipe in time and further achieve the purposes of real-time measurement and real-time display. Compared with the manual measurement, the real-time measurement device has the advantages of high precision, relatively-simple structure, relatively-low manufacturing cost and high work efficiency.