Due to variations of misalignment and clearance, the parameters of the contactless transformer (CT) change a lot, creating great challenge in the design and control of the inductive power transfer systems. In this paper, the characteristics of a S/P compensated resonant converter is analyzed by introducing relative self-inductance coefficient and relative mutual-inductance coefficient to describe the parameter variations for CT. Based on the voltage gain and input impedance analysis, the voltage gain value at the intersection point and the inductive region of the input impedance are found. Furthermore, a fully tuned point is selected fulfilling zero voltage switching (ZVS) condition for the full-parameter ranges of load and CT. A 7.5 kW prototype with constant frequency control is developed and fabricated to verify the analysis.