A white light interference system was developed with a speed-variable scanning technology to improve signal utilization precision and short measuring time for a large step structure measurement. A Fourier transform and unilateral step evaluation algorithm were performed for processing the scanning interference images. A calibrated standard step height of 9.976±0.028 μm was measured by the white light interference system using the speed-variable scanning method, the measuring time was 35 s, which was much shorter than a conventional measuring time of 222 s. A 10-times-repetitive-measurement shows a result of 9.971 μm with a standard deviation of 0.007 μm, illustrates that the system has accuracy and high-efficiency in the measurement of large step structure.