In order to study the silicon based semiconductor's electro-optic-thermal muti-field coupling characteristics and electric modulation problems,both the Poisson equation and the carrier continuity equation were introduced to calculate the carrier concentration distribution in the carrier transport procession. Drude Lorentz relation and K-K relation were also employed to discuss the effect of the carrier concentration on the refractive index and absorption coefficient. The heat deposited items were obtained by calculating electromagnetic dissipation. The coupled semiconductor basic equation,electromagnetic wave equation and energy equation were solved by using finite element method. With the effect of external voltage,initial concentration of carrier and heat transfer coefficient,the change of dielectric properties,optical transmission behavior of silicon based semiconductor were also analyzed by coupling solution and analysis. The results show that the reflective optical field mode of the semiconductor P area increases with the increasing of the applied voltage,and decreases with the increasing of the heat transfer coefficient. Using this mechanism,a scheme of electric thermal modulation for the space distribution of the reflection intensity was presented.