To improve the accuracy of long trace profiler for measuring the surface profile of tube-shaped super-smooth mirrors, some common errors and correcting methods are studied and summed up. The errors caused by the tilt and decenter between the rotating axis of rotary table and the axis of tube-shaped mirror under test during measurement will influence the result very much. These errors are in detail analyzed, and a correction method through data processing is presented. Then, a data processing code is programmed, and a numerical-simulation experiment is given to decide the properties of the code. Experimental results indicate that the code can remove the tilt and decenter errors between rotary table and mirror under test effectively, and improve the accuracy of tube-shaped mirror measurement using long trace profiler. When there is 5 μm decenter and 1′ tilt between the rotary table and mirror under test, using the code to restore the surface profile at the order of 50 nm, the restoration accuracy is root-mean-square (RMS) 2.8 nm and peak-to-valley (PV) 18.5 nm.