The invention discloses a defect detection method based on transmission structured light, and is used for detecting the defects of a detected object with high transmissivity. The method comprises thefollowing steps that: firstly, generating stripe structured light, projecting the stripe structured light to the surface of the detected object, and after the stripe structured light is transmitted through the detected object, generating deformed stripe structured light; collecting the deformed stripe structured light, and utilizing a modulation degree technology to convert a collected light intensity graph into a modulation degree graph; and combining with a subsequent algorithm to obtain the surface defect information of the detected object. The method is especially suitable for the defect detection of a large-size large-curvature glass cover plate. Compared with a reflection system, a transmission system which is put forward by the invention eliminates the influence of parasitic stripes, improves the stripe contrast ratio of a collected image, improves the signal-to-noise ratio of an original image and improves a measurement result. In a whole detection process, a complex calibration process is not required, the height information of the object does not need to be subjected to integral reconstruction, errors brought by an integral algorithm are avoided, and the method has the characteristics of being quick, easy in operation, simple and practical.