Abstract: Based on the theoretical model of Rossler reaction system, a new dynamical system under external periodic perturbation modulation is constructed. The dynamical behavior of oscillatory state in the new system is investigated by using of the inverse operator method and the numerical analysis method because the inverse operator method is of high precision, quick convergence for the solution of nonlinear equations. The results show that the dynamical behavior of the system takes place notable changes and takes on many new evolution patterns under the external modulation of the periodic perturbation. For examples, the single periodic oscillation in the system which perturbation is not added is evolved to multi-period oscillatory states, such as period two (2P), period four(4P),…, 2nP and chaos when the system is modulated by periodic perturbation. It is found that the parameter of the perturbation phase (PP) is the most sensitive and the highest efficient in the modulation process if only one parameter is modulated while others are kept constant. In the same time, the new evolution patterns of the system (multi-period oscillatory state and chaos) will take on in the different numerical regions of the PP, and the small number change of the PP can influence internal construction of each evolution pattern although evolution patterns of the system don′t change.