An improved phase-measuring deflectometry (PMD) is presented for the aspheric surfaces test. We explore this method from the Ronchi test in a reverse way. With this concept, a camera aperture is placed near the center of curvature of the test mirror, and fringes are displayed on a liquid crystal display screen. The fringes reflected off the test mirror are observed by the camera. By analyzing the captured fringes, the deviations of the test mirror from its ideal shape are obtained and the aspheric surface under test is reconstructed. Compared with traditional PMD, this method needs only to determine reflected rays and doesn't need to know the corresponding incident rays by calibrations, moving screen, or approximation. Both a computer simulation and preliminary experiment have been carried out to demonstrate the validity of the improved PMD. This improved PMD provides a new tool to measure aspheric surfaces quantitatively in full field for optical manufacturing.