HLA (high level architecture) is the standard for modeling and simulation put forward by the American Department of Defense. Time management is an important component of HLA while GALT (greatest available logical time) algorithm is RTI (runtime infrastructure)抯 critical technology in implementing time management. An improper GALT algorithm can easily result in a deadlock so that the whole federation can not advance any more. On the basis of the GALT algorithm introduced by Frederick Kuhl, the principles of deadlock are discussed and some important results are revealed in this paper. If deadlock occurs in a simulation, all federates must have the same GALT and the same output time respectively, and GALT is also equal to output time, and a federate whoselookahead is greater than zero must suspend because of a NMR or NMRA request, other than a TAR, TARA or FQR request. Finally, a GALT algorithm without deadlock is also brought forward in this paper that is calledStature-Measuring, and this algorithm can provide reliable technology support to develop time management services of RTI.