Deflectometry offers distinct advantages for assessing the forms and defects of complex optical surfaces， attributed to its straightforward measurement structure， high dynamic range， and superior anti-interference capabilities. However， the intricate measurement operations， numerous influencing factors， and extensive data transfer chain associated with deflectometry significantly constrain its practical applications in engineering. Accordingly， the fundamental principles and historical development of deflectometry are delineated， and the primary measurement procedures， comprising structural design， system calibration， pattern coding， object-image matching， and integral reconstruction， are described. Several critical factors influencing measurement accuracy are examined， including camera model simplification， height-slope ambiguity， position-angle uncertainty， and the rank-deficiency in form reconstruction. Subsequently， a discussion of the primary application scenarios and future trends of deflectometry is provided， with the objective of assisting researchers and graduate students in mastering deflectometric methodologies， managing key strategies to enhance measurement accuracy， and fostering technological advancements and industrial growth within China’s precision engineering and advanced manufacturing sectors.