The　safety　of　supporting　structures　for　high-speed　trains　has　motivated　many　researchers　to　develop　an　effective　method　for　reliability　analysis　of　the　structure　as　a　whole.　In　this　study,　a　unitless　model　for　system　limit　state　function　is　developed,　which　enables　the　system　reliability　analysis　of　the　CRTS　II　track　slab　on　viaduct　with　multiple　failure　modes.　The　method　of　moments　is　employed　to　determine　the　system　reliability,　and　the　influences　of　important　variables　on　the　system　reliability　of　the　track　slab　are　investigated.　It　is　found　that　the　reliability　of　the　CRTS　II　track　slab　would　be　overestimated　if　only　individual　failure　modes　are　considered　independently,　which　vindicates　the　importance　to　conduct　system　reliability　analysis　for　CRTS　II　track　slab.　It　is　also　found　that　the　randomness　of　the　number　of　load　cycles　significantly　affects　the　system　reliability　of　the　track　slab.　The　merit　of　the　developed　unitless　model　for　system　limit　state　function　is　its　facilitation　of　the　efficient　and　accurate　analysis　of　system　reliability　for　the　CRTS　II　track　slab　with　no　conditions　and　constraints.