The parameter of isolator used in high position story isolated structure under earthquake is optimized. The multi-degree of freedom system is modeled by two degree of freedom system for the story isolated structure, and the ground motion is represented by white-noise excitation. The optimization target is to minimize the sum of vibration energy in frequency domain of the higher and lower structures in the story isolated structure system. The explicit expression of optimal stiffness coefficient and damping coefficient of isolator derived. The theory expression demonstrated that the optimal stiffness coefficient and damping coefficient of the isolator is closely related to the mass ratio of the higher structure to the lower structure. In the numerical example, using the Kanai-Tajimi filtered white-noise ground motion model, the appropriate parameters of isolator are achieved through extensive parametric studies firstly. Then, through comparative study, it can be found that the results of parametric studies are consistent with the optimal theoretical values of isolator obtained by means of theory expressions. While the structure excited by actual earthquake records, the seismic response of structures are coincided with each other for multi degree of freedom system and two degree of freedom system. The results show that the explicit formulas of isolator can help engineers in application of high position story isolated structures.