A surface profile measuring device, based on the principle of long trace profiler, is designed and established to measure the surface profile of Wolter type-I mirror. In order to obtain higher surface profile measuring accuracy, two particular improvements are made to the surface profile measuring device. The nonlinear error and the motion error of the translation slide can be eliminated by using a penta prism, which possesses an optical property all its own. The ideal measuring accuracy of the surface profile measuring device is improved by using position sensitive detector instead of CCD detector. The calibration and sample measurement experiments are done and the experimental data are compared with the old data. The result shows that the new measuring device can achieve an accuracy of 1.7 μrad for slope root-mean-square error and 56 nm for peak to valley height error. Its measuring accuracy has been significantly improved. This can meet further requirements of precision fabrication for Wolter type-I mirror.