Computer generated holograms are widely used in optical testing and metrology. The primary role of the CGHs is to generate reference wavefront with any desired shape. Optical or electron-beam writers are commonly used for CGH fabrication. Limitations from the hologram fabrication processes cause errors in the reproduced wavefront. Errors in duty-cycle and etching depth have direct impact on both the amplitude and phase functions of the reproduced wavefront. A study using scalar diffraction model to simulate CGH fabrication errors and their effects on wavefront amplitude and phase functions are presented. Experimental analysis confirms the theoretical model. An example is given at the end to demonstrate one of the many applications of the wavefront sensitivity functions in CGH error budgeting for optical metrology.