Using Markov model to evaluate reliability of the tracking, telemetry and command (TT&C) and communication system is very difficult if there are many facilities in system, due to the fact that Markov modeling techniques suffer from the state explosion problem. In light of this, a reliability analysis method based on Krylov subspace is proposed; the main idea of this method is projecting the initial problem to a smaller subspace for the obtaining of an approximating result. Examples prove that the proposed method performs better than Ross method and Forward Euler Method, and it can achieve a good efficiency and accuracy.