A new parameter identification method for a class of hysteretic nonlinear system is presented. The integration property of the BoucWen model, which plays an important role in later linear and hysteretic parameter identification, is analyzed through constructing appropriate periodic inputs. System states and equivalent disturbance are observed by extended state observer to develop equation set and by solving linear equation set, linear and nonlinear parameters are identified individually. The effectiveness of the method is validated via simulation. Finally, the proposed method is applied to a class of piezoelectric system for identifying hysteretic nonlinear system model, which reflects the characteristics of the real system well.