Abstract: Communication is driven by agents’ mental states. It is an information exchange process among agents. Communication allows agents to perceive the environment and to strengthen their capacity to take actions. It is not only an embodiment of society, but also an important way of cooperation and negotiation. Based on BDI state of thinking, ＆ semantic description of KQML, a common communication language for agent is given. The description eliminates the ambiguity of its semantics and avoids internal conflicts in the state of thinking due to communication. Also discussed is the transformation between communication and BDI, which is applied in dynamic and open processes of negotiations. The work of Finin, Cohen et al is extended and improved.