A quick, reliable and accurate method and device for measuring an optically reflecting surface, enabling quantifying of the curvatures and/or slopes and raised parts of the optically reflecting surface without risk of deteriorating the measured surface and adapted to measurement of large-dimension surfaces. The system and method for measuring the geometry of an optically reflecting surface to be measured S includes observing with a camera (2) the image of the surface to be measured S set in a measuring space (1), then interpreting the image in quantitative values characterizing at least one geometric quantity of the optically reflecting surface to be measured S.