Based on Ansari’s strain transferring analytical model for fiber optic sensors and basic theories in elastic mechanics, a universal basic optical-mechanical transformation theoretical equation which is the base for standarzied design and precision analysis for embedded fiber Bragg grating (FBG) strain sensors is established. In course of establishing the equation, the axial mechanically coupling mechanisms within sensor complex and with sensed environments are reflected, each boundary condition and displacement coordination condition for strain transferring analytical mode are considered, and all sensor geometrical parameters are taken into account. Experimental study on a sensor sample has validated the rough reliability of proposed theoretical equation.