Abstarct: Due to many problems of physics which are modeled by differential-algebraic equations .It is appropriate to find the answers with high accuracy. In recent years numerical methods are used to solve the equations. But these methods are just suitable for the problems with low index and they can not be used for high index so it is necessary to find answers with a high accuracy. In this thesis we are going to solve the differential-algebraic equation by using the semi analytic methods. In order to solve the differential-algebraic problems we can use the index reduction methods, then we can solve its income system with the semianalytical Variational iteration ,Adomian decomposition and Homotopy perturbation method. The Variational iteration method provides a sequence of function which converge to the exact solution of the problem. The Adomian decomposition method and Homotopy perturbation method generates an infinite series with converge to the exact solution. The numerical results of solving several examples of high-index shows the efficiency and neccessity of using these methods.