Abstract: his paper discusses the auto-pilot expert system of large outdoor mobile robot(APESMR).A due hardware environment with sensors,computers and vehicle actuator and their relationship is introduced.The general structure of the auto-pilot expert system on a mobile robot,the building and using of knowledge bases,and the operating mechanism of some function modules are stated respectivelly.This system has been applied to a unmanned land vehicle which is a modified WZ-503 armoured personnel carrier.It has not only replaced compeletely driver's all kinds of operations but also been successful in many complicated tasks such as autonomous navigation,mission planning,auto obstacle avoiding.dynamic target tracing,and retro-tra-verse etc.