We propose a new optical profilometer for three-dimensional (3D) surface profile measurement in real time. The deviation angle is based on geometrical optics and is proportional to the apex angle of a test plate. Measuring the reflectivity of a parallelogram prism allows detection of the deviation angle when the beam is incident at the nearby critical angle. The reflectivity is inversely proportional to the deviation angle and proportional to the apex angle and surface height. We use a charge-coupled device (CCD) camera at the image plane to capture the reflectivity profile and obtain the 3D surface profile directly.