A surface measuring device includes a rotary platform, a shifting lever, a measuring module, and a control module. The rotary platform carries an object under test and rotates the object under test at a rotating speed. The shifting lever is above the rotary platform. The measuring module disposed on the shifting lever moves to measurement positions on the shifting lever and performs a surface height measurement at a sampling frequency to sampling points on a surface of the object under test when located at one measurement position. The control module selectively adjusts the rotational speed for the rotary platform or the sampling frequency for the measuring module according to the measurement position of the measuring module on the shifting lever in order to fit a distance between the sampling points on at least one part of the surface of the object under test to a sampling rule.