Abstract: It is well known that experimental methods of stress analysis are of great use for studying composite materials and structure,and optical methods have the advantage of yielding full-field quantitative results.In this papar.the application of transmission photoelastic techniques to the study of composite specimens and the survey of historical developments of photoorthotropic elasticity for composites are mainly introduced during the last two decades,The fabrication of the model materials and photoelastic calibration for determining the three independent photoelasic constants in many countries are mentioned in detail and a summary of the early prgresses about birefringant orthotropic model materials in China are presented.Then,the basic principles governing the photoelastic response in birefringent orthotropic compos are briefly reviewed.The contents of various stress-optic law and strainoptic law are discussed and compared with each other.Seven methods of separating the principal stresses in birefringent composite models are proposed.Finally,the advantages and problems of photo-orthotrpic elastic techniques are appraised.It is reasonable to expect that further developments in photor-orthotropic elasticity will lead to establishing a method to solve problems of engineering importance.