Evaluation of step height standard with high accuracy is realized using a nano-measuring machine (NMM) integrated with a focusing sensor. The measuring range of the system is up to 25 mm×25 mm×5 mm. The operating principle of the NMM is described. NMM has high accuracy positioning and scanning performance through real-time measurement and feedback of built-in laser interferometers and angular sensors. The focusing sensor is only used as a zero point sensor, intersected at the same point with the three laser beams, which eliminates Abbe error. The output signal of the focusing sensor is introduced into the digital signal processing (DSP) controller of the NMM. The NMM will also measure data in z direction at the same time, which minimizes the influence of the focusing sensor's nonlinearity. According to the international standard of ISO 5436-1:2000, a calibrated step height is measured. The root-mean-square (RMS) deviation of 14 times measurements is 0.237 nm.