As　a　data　source,　log　files　recorded　the　basic　contents　of　intrusion　detection　system.　The　most　popular　and　effective　way　to　perform　host-based　intrusion　detection　is　to　audit　log　data　and　take　some　effective　measures　to　decrease　the　loss.　Integrating　original　log　analyzing　technique　with　mobile-agent,　LASL　implements　a　host-based　log　analyzing　system.　Compared　with　other　log　analyzing　tools,　LASL　has　intellectualized,　automatic　and　distributed　characters.