With　the　rapid　development　of　integrated　circuits,　a　complete　system　of　integrated　Circuits　contains　multiple　clocks　in　a　chip.　Under　the　control　of　different　clock　domains,　data　can　become　metastable　state　between　transfers　or　storage.　This　paper　describes　one　of　the　effective　methods　to　solve　the　problem　about　the　metastable　state,　the　method　is　asynchronous　FIFO.　We　study　Synchronous　FIFO　and　Asynchronous　FIFO　in　this　paper.　The　article　analyses　the　reasons　for　the　emergence　of　sub-stability　metastable　state　and　how　to　use　the　Gray　Code　to　solve　metastable　state　problems　effectively.　We　can　generate　empty/full　status　bits　via　Gray　Code　pointer,　it　can　effectively　reduce　the　probability　of　metastable　state.　This　paper　has　the　significance　of　guiding　the　use　of　FIFO.　©　2023　IEEE.