The interference microscope measurements with white light scanning interferometry (WLSI) and phase stepping interferometry (PSI) have been improved by optimizing the experimental conditions such as vertical distance between the objective and the surface under test (z), the tilt angles of the incident light beam with the surface and incident light intensity (I). Finally an accurate surface parameters measurement is obtainable. A genetic algorithm code has been developed to determine the best values of experimental conditions instead of manual adjustment by the operator. The combined uncertainty has been successfully reduced from 3.01 nm to 0.84 nm for the WLSI roughness measurement. While it has been reduced from 0.18 nm to 0.08 nm for the PSI step height measurement.