Sonic　crystals　are　composite　materials　made　of　periodic　distributions　of　inclusions　embedded　in　a　matrix.　Due　to　the　periodicity,　these　materials　may　exhibit　complete　acoustic　band　gaps　within　which　sound　and　vibrations　are　forbidden.　In　this　paper,　the　band　gap　characteristics　of　a　2-D　square　array　of　hollow　cylinders　and　spit-ring　hollow　cylinders　embedded　in　air　are　investigated　by　COMSOL(R)　finite　element　method,　and　then　verified　by　plane　wave　expansion　method.　The　results　are　very　consistent,　proving　that　COMSOL(R)　can　be　employed　for　the　full　characterization　of　the　structures.