In　this　paper,　precise　integration　in　a　symplectic　system　is　used　to　analyze　the　stop-band　characteristic　of　the　dielectric　layer　PBG　structure　in　a　waveguide.　The　transverse　section　is　made　discrete　by　using　edge　elements.　The　stiff　matrices　of　a　dielectric　layer　and　an　air　layer　can　be　calculated　by　precision　integration　based　on　Riccati　equations　in　a　Hamiltonian　system.　The　export　stiff　matrices　of　a　period　can　be　obtained　by　a　combination　of　substructures,　and　then　the　whole　structure　can　be　solved.　The　stop-band　characteristic　of　a　dielectric　layer　PBG　structure　in　a　waveguide　is　obtained　and　the　effects　of　the　size　of　period　and　the　number　of　periods　are　discussed.　The　examples　presented　show　that　this　method　is　precise　and　efficient.