To choose proper laser and CCD for studying of wavelength phase-shifting interferometry, the main random errors are numerically simulated in the system based on direct algorithm and Monte-Carlo method. The basic structure of Fizeau wavelength phase-shifting interferometer and theory of measurement are introduced, the errors by vibrating, air turbulence and instability of laser frequence are analysed and the model is set up. Then, combined with the results of numerical simulation, the correspondence between each error and its measuring result is abtained, and proper laser and CCD are determined, simultaneously the error distribution is given. By setting up the interferometer and measuring, the results show that repeatability root-mean-square (RMS) error is better than 0.07 nm, which reaches the requirement.