The invention provides a system and a method for detecting a surface defect of a glass panel. According to the system and the method, a single lens and a telecentric light path are combined with phase measurement deflectometry. Through setting positions of coding surface structural light display equipment, a beam splitter mirror, a to-be-detected surface of the glass panel and an image acquisition device in a space, a reflection law is satisfied. A lens is arranged between the coding surface structural light display equipment and the beam splitter mirror. Furthermore the coding surface structural light display equipment is arranged above an object space focal plane of the lens. Through computer controlling, standard N-step phase shift surface structural light which is perpendicular with each other is generated and transmitted to the to-be-detected surface of the glass panel. After image acquisition, back-end image processing equipment performs processing for obtaining modulation degree distribution, optimal gradient distribution and optimal height distribution of deformation surface structural light. The system and the method settle a problem of phase and height information inaccuracy caused by system ambiguity in defect detection by a traditional system based on the phase measurement deflectometry, and furthermore improving precision and accuracy in performing surface defect detection on the glass panel.