Abstract: Based on Block-Pulse Functions and Shifted Chebyshev Polynomials (SCP), the orthogonal functions--Piecewise Multiple Chebyshev Polynomials (PMCP) is introduced in this paper Main properties and basic operational rules of PMCP are studied. The integral operational matrix, the product operational matrix and the element product operational matrix are proposed. PMCP has been successfully applied to parameter identification of linear time-varying systems. Simple, rapid, accurate and recursive algorithm is obtained via PMCP. The results of the illustrated examples show that the algorithm presented is better than that via SCP for approximating piecewise continuous functions or the functions having severe variety, such as P. R.B.S.