This paper addresses the secure control problem of cyber-physical systems (CPSs) under Denial-of-Service (DoS) attack with power constraint. The purpose of the attacker is to degenerate the control performance of CPSs at the reduced cost of attack power. Unlike the existing works developed under the assumption of time-invariant channel states, the sensor-to-estimator communication channel under consideration is a standard block fading communication channel. By taking the angle of the DoS attacker, an optimization problem is formulated to deal with both the linear quadratic control cost of the CPS and the expenditure of attack power. Then, the formulated problem is transformed into a Markov decision problem. As it is difficult to provide an analytical expression of optimal attack power, the objective function is approximated to derive an analytical expression of the suboptimal attack power. Next the attack strategies for two specific communication schemes, namely, the capacity achieving coding scheme and the forward error correction scheme, are studied. Finally, the validity of the proposed attack strategy is demonstrated by an illustrative example.