This paper considers the $H_{infty}$ control problem of networked control systems, respectively, for the two cases that system state is available and unavailable. It is assumed that there exists a communication network in the feedback loop, and multiple data packet dropouts may happen. An estimation method is introduced to compensate the lost data. And then, the design of $H_{infty}$ control is considered for the states available and states unavailable, respectively, and some sufficient conditions are derived such that the closed-loop systems are exponentially mean-square stable with prescribed $H_{infty}$ disturbance attenuation level.