Thehomoclinicbifurcationsinfourdimensionalvectorfieldsareinvestigatedbysettingupalocalcoordinatesnearthehomoclinicorbit.Thishomoclinicorbitisnonprincipalinthemeaningsthatitspositivesemi-orbittakesorbitflipanditsunstablefoliationtakesinclinationflip.Theexistence,nonexistence,uniquenessandcoexistenceofthe1-homoclinicorbitandthe1-periodicorbitarestudied.Theexistenceofthetwofoldperiodicorbitandthree-foldperiodicorbitarealsoobtained.