The implemented BDI (belief, desire and intention) Agent systems used the three major mental attitudes as data structures, rather than as model operators. So th ere still remains a large gap between theory and practice. In this paper, the au thors present an improved programming language——AgentBDI, concerning the i nterpreter of dMARS (developed multi-agent reasoning system) after in-depth st udying PRS (procedure reasoning system) and dMARs, and provide AgentBDI's gramma r and operational semantic using a classical example of DAI. The authors also pr ovide an improved interpreter of BDI Agent based on AgentBDI. AgentBDI can b e viewed as an abstraction of dMARs, and allows BDI Agent programs to be written and interpreted in a manner similar to the logical programs.