Aiming at the problems of frequency response,transmission capacity and efficiency optimization in novel EM field resonant coupling power transmission system,a mathematical equivalent model is proposed based on coupled mode theory.By introduction of mode coupling factor and quality factor,the influences of different physical parameters on system performance are discussed to obtain best working conditions.Moreover active power on the load and system transmission efficiency as a function of distance between oscillators is deduced.Then,planar disc resonant coils are proposed taking into account shortcomings of coaxial helical coils such as large volume and instability of resonant points.It is shown by results that blindness for designing actual system is reduced and overall efficiency capacity is improved.