For nonlinear system filtering problem,Kalman filter cannot be used.Though the extended Kalman filter can be used in nonlinear system,but the outcome of the filter is a partial estimation and the system is not very robust.To get better state estimation,a filtering method,named Unscented Kalman filter,is introduced.The idea of the filter is: the UKF generates better estimates of mean and the covariance of the state,leading to higher accuracy based on the unscented transformation.Compared with the filtering estimate results given from a time series state estimation example based on Mackey-Glass Model,the simulation shows that UKF not only leads to more accurate results than EKF,but also can avoid computing Jacobi matrix.