Motivated　by　the　defense　of　a　power　grid　control　center　against　cyber-attacks,　this　research　considers　the　optimal　allocation　of　defense　resources　for　defending　a　parallel　system　consisting　of　identical　elements.　To　enhance　the　system　survivability,　the　defender　distributes　its　limited　resources　to　provide　redundancy,　disinform　the　attacker,　and　protect　system　elements.　Correspondingly,　the　attacker　allocates　its　limited　resources　to　intelligence　actions　and　impact　contests.　The　defender　determines　the　optimal　number　of　genuine　elements　and　false　elements　to　deploy　and　the　optimal　amount　of　resources　used　for　disinformation　actions.　The　attacker　seeks　to　maximize　the　system　damage　by　taking　the　defender＇s　strategy　as　given　and　allocating　its　resources　optimally　into　intelligence　actions　and　impact　contests.　Two　types　of　parallel　systems　are　considered:　(1)　where　the　system　damage　is　defined　as　the　probability　of　system　failure,　and　(2)　where　the　system　damage　is　defined　as　the　unsupplied　demand　of　the　system.　Due　to　the　complexity　of　the　optimization　model,　we　analyze　the　optimal　defense　strategy　under　various　parameter　settings　via　numerical　methods.　The　results　provide　useful　insights　on　how　to　defend　such　a　system　under　different　situations.