Resonant wireless power transmission has the advantages of long transmission distance and high efficiency. Series — series (SS) transmitting and receiving system is suitable for small load research. In this paper SS-type circuit is analyzed and discussed by using equivalent circuit theory. The mathematical models of the transmission efficiency and output power are derived. The influencing factors, such as resonant frequency, transmission distance and load resistance, are analyzed in MATLAB software by using the optimization factor ζ as comprehensive evaluation index. Then the optimal parameters are calculated with a supply voltage of 15 V. The result can provide reference for the actual design of SS — type wireless power transmission system.