The existence and uniqueness of periodic solutions are established for a full nonlinear second-order periodic system F(t,?,?)=0 under some natural structure conditions and typical assumption by using the new method based on the viscosity solution theory.

• 在适当的结构条件和标准假设下；采用基于粘性解理论的新方法；证明了完全非线性二次系统:F(t；x；?；?)=0周期解的存在唯一性.