In the past decade, security issues of Cyber-Physical Systems (CPSs) have drawn enormous attention due to the wide spectrum of applications of CPSs and the serious impact of malicious cyber attacks on CPSs. In this paper, an observer-based feedback control method is used. The guaranteed cost control for a class of CPSs under stochastic DoS attacks on the channel between the sensor and the controller (S-C) is studied. A stochastic interference model is established within an unified framework to reflect the stochastic occuring behaviours of SINR-based DoS attacks and inherent packet dropouts. The guaranteed cost controller is designed to exponentially stabilize the CPS under stochastic DoS attacks in mean-square and the corresponding cost function is less than a specified upper bound. Simulation example is used to demonstrate the effectiveness of the guaranteed cost controll strategy.