Inthispaper,maximum-likelihood(ML)anditsrelaxationalgorithm,whichareusedtoidentifythemathematicsmodelofanunderwatervehicle(UV),arcdiscussed.Withthetrialdataofzigzagtests,thehydrodynamicderivativesoftheUVwereestimated,andtherelaxationalgorithmisconfirmedtohavebetterastringencyfromthecontrastbetweenthetwomethods.Thenasimulationenvironmentbasedontheseparametersisestablishedtoverifythevalidityandeffectofthesemeth-ods.Theresultshowsthemodeliscredibleandthemethodsareveryusefulfortheresearchofmaneuverabilityandadaptivecontrolofunderwatervehicles.
