Chinese　Word　Segmentation　is　an　important　task　in　natural　language　processing　for　languages　without　word　delimiters.　In　this　paper　we　analyze　the　key　issues　in　Chinese　word　segmentation　from　three　degrees:　the　limitation　of　supervised　segmentation,　the　shortcoming　in　unsupervised　segmentation,　and　the　relationship　of　OOV,　ambiguity　and　word　segmentation　result.　The　analysis　shows　that　supervised　and　unsupervised　segmentation　are　not　suitable　for　domain　word　segmentation.　And　the　problem　of　ambiguity　will　be　more　serious　than　OOV　in　practical　application.　Copyright　©　2013　Binary　Information　Press.