The consensus error calculation of the multi-agent systems (MASs) with system noises and communication noises is considered in this paper. Each agent is modeled by a continuous-time linear time-invariant dynamics and the communication topology is described by an undirected graph. It is supposed that the agent can obtain its own state accurately and receive the state of the neighbor agent with noisy disturbance. The agent estimates its neighbors' state based on the noisy measurement receiving from its neighbors. The distributed control protocol is designed by employing the agent's own state and the estimated state of is neighbor agents. Due to the existence of the system noises, the MASs can not reach consensus. The consensus error will be calculated via a solution of a Lyapunov equation.