The phase dispersion effect of intercavity elements plays an important role in the femto-second technique. This paper describes an experimental method for measuring the phase dispersion of multi-layer wide band high reflective dielectric coatings by means of multi-beam interference. The phase second derivative of reflective coatings is calculated. Experimental results show that the phase shift and the phase second derivative are closely related to the manufacturing process and design of the wide band multi-layer reflective coating.