Abstract: The purpose of the study on the nonlinear static analysis is to simplify the practical engineering analysis and use its result to guide the practical engineering design. To achieve this aim, a simplified equation is proposed in this paper and a parameter study is conducted to get the rational coefficient values in the equation. At the same time the target displacement of a MDOF (Multiple degree of freedom) structure under design earthquake can be obtained from its equivalent SDOF (Single degree of freedom) system. The analysis of a practical engineering structure with the simplified equation proposed in this paper is more efficient than with the traditional one, and the complex nonlinear dynamic history analysis procedure is avoided.