In recent years, fiber optic sensors applications have been extended from the laboratory research and development stage to practical and industrial use. A great deal of research effort has been focused on improving functionality of these sensors and also to overcome their limitations and challenges. Coupled sensitivity of optical fiber sensors to structural strain and temperature has been a long lasting problem for reliable measurements in environments where both parameters are varying. Many methods have been already investigated to overcome this challenge. The most recent ones have resulted the use of Superstructure FBGs with on-fiber thin metal film that have the ability of simultaneous measurement of temperature and strain. This thesis is conducted in order to prepare a numerical model for prediction of behavior of these SFBGs and also to prepare a tool for designing these sensors. For this propose Opto-Mechanical modeling of FBG and SFBG sensors are presented. Then finite element modeling of SFBGs with on-fiber metal film and numerical solution of differential equation ruling their optical behavior is also presented. The results of numerical simulation show good agreement with former experimental results. By completing the simulation process and validating the results, effect of geometrical parameters of the coating on final spectrum of these sensors is studied. The geometrical parameters considered in this work are coating period, coating duty cycle, and coating thickness. The results of numerical modeling show that the side peak spacing is only depend on the coating period. Coating duty cycle and coating thickness can affect both sensitivity of Bragg peak and reflection intensity of side peaks. Furthermore it can be seen that Bragg peak sensitivity does not depend on coating period. The method of simultaneous measurement of temperature and strain for a sample sensor is also explained. Primary experiments which have been conducted in order to evaluate manufacturing possibility of these sensors are also presented and finally some key points resulted from this work are given for a better design of SFBG sensors. Keywords: Fiber optic sensors, Fiber Bragg grating, Simultaneous measurement, Numerical modeling, FBG, SFBG