To provide the basis of ecology and biodiversity conservation in coastal islands,We conducted floristic spectrum,diversity index,principal coordinate analysis and cluster analysis to reveal distribution patterns and floristic relationships of coastal islands (chose from Bohai,Huanghai,Donghai and Naihai in different latitude area) in China.Results showed that:(1) with the decrease of latitude,a decreasing trend can be observed on the proportions of temperate elements at genus-level,while those of tropical elements showed contrary patterns,which may be strongly corelated with their different ecological characters and energy distribution;(2) Compared with other coastal islands,floristic Shannon index (1.887-2.197) and Simpson index (0.780-0.865) have no obvious difference.Pearson correlation is significant at the 0.01 level by correlation analysis,and the coefficients are between 0.199 and 0.997.(3) Two-dimentional scatter plot of PcoA and cluster dendrogram based on the floristic spectrum demonstrated floras of 22 coastal islands were divided into 5 groups,North-south latitude distribution pattern and similarity of the floristic of 22 coastal islands in China was revealed accordingly.