Given a linear variable coeffcient DAE, the logarithmic norm of a pencil related to the original pencil (A(t)
B(t)), allows us to determine the contractivity of ||A(t)x(t)||. When stable Runge-Kutta methods are used for DAEs, the contractivity for ||An+1 Xn+l|| is no longer maintained for all stepsize. In this paper, the author define for Runge-Kutta methods.