A primary control strategy of wireless power transfer system based on load identification method is proposed to meet the challenge related to wireless power transmission, system robustness and difficulties in primary controller because of the uncertainties of secondary side parameters. Take a Series-Series-type WPT system as an example, a method of online parameter identification based on switching operating frequency is proposed and a mathematical model about the load and the mutual inductance is established. Based on the proposed algorithm for online identification of parameters, a primary control strategy for wireless power transmission system is proposed. The output voltage can be controlled and power can be transmitted after the mutual inductance and load are recognized. Experimental results have verified the proposed online load identification method and primary strategy which has been demonstrated that the method is accurate and reliable for uncertain loads and mutual inductance. The method can be used in other type WPT systems to improve the system performance with precise control as well.