A slow-light system composed by a microsphere resonator and a section of bitapered fiber is characterized theoretically in this article. Theoretical analysis and numerical simulation on the input and output characteristics and the transmittivity of the microsphere resonator were carried out. The directional coupling theory was used to analyze the input/output characteristics of single microsphere resonator and parameters in the overcoupling state, including the relationships between the effective phase shift, transmittivity, effective time delay, light velocity, and the speed of light. The coupling coefficient distance was studied by theoretical analysis and numerical simulation. The theoretical analysis and simulation optimization of the slow-light gyroscope were carried out to obtain the optimized radius of microsphere resonator and distance between microsphere resonator and bitapered fiber. Through theoretical investigation and mathematical simulation, transmission characteristics and time delay mathematical expressions of the microsphere resonator were obtained. Theoretical analysis and simulation of the fiber optic gyroscope sensitivity showed that slow-light improved the accuracy of the interferometric fiber optic gyroscope. [ABSTRACT FROM AUTHOR]