It is rather important to study deadlocks in the High Level Architecture (HLA) for correctly comprehending time advancing mechanism in HLA standards,designing time management services in Runtime Infrastructure (RTI),and developing HLA/RTI simulations based on logical time.This paper investigates deadlocks in the HLA time management from different aspects,including deadlocks resulted from zero lookahead,from time advance services,and from time management algorithms as well as the resolution of deadlocks.A series of interesting phenomena are also explored,and varieties of cases in which deadlocks must happen or must not happen are also demonstrated.Particularly,the paper brings forward a rather common principle called Water Surface Rule.This rule shows that all programs cannot advance further and all of them are in relatively quiet status when deadlock occurs,which seems to be the calm water surface.In HLA/RTI simulations,all programs in deadlock status have the identical Greatest Available Logical Time (GALT) so that none of them can advance logical time any further.