There are 32 000 km of coastal line and 2×10⁶ hm² of beach land in coastal area, China. Hangzhou Bay coastal wetland is the intersection of north and south coastal wetlands in China, and which is implied that the research is of high value in the view of science. It is well known that plant distribution and bio-diversity are influenced strongly by soil salinity of beach in coastal wetlands. Relationships between plant species distribution, bio-diversity and soil salinity have been studied in many sites in past several decades, yet few focusing on soil base cations composition of beach and their effects on plant distribution and diversity. In this paper, soil base cations composition and distribution, plant species composition and diversity in 50 plots were monitored using method of line transects with random sampling in Hangzhou Bay coastal wetlands, and the effects of base cations on plant species distribution and diversity were analyzed using Detrended Canonical Correspondence Analysis (DCCA), stepwise regression and linear regression. The 4 main base cations concentrations (means ± SD) were (3.66±1.58) g/kg (Ca²⁺), (1.83±1.25) g/kg (Na⁺), (0.56±0.23) g/kg (Mg²⁺), (0.22±0.12) g/kg (K⁺), respectively. And the concentration of Ca²⁺ was accounted for 61.97% of total base cations concentrations. While the base cations concentrations of coastal beach out of inning dam ((4.87±0.41), (2.19±0.26), (0.65±0.12), (0.28±0.07) g/kg, respectively) were higher than in inning dam (P<0.05). Meanwhile, 17 species were found in 50 plots, herbs mainly including typical beach plants, such as Scirpus mariqueter, Phragmites communis, Spartina alterniflora, etc., and shrubs including Tamarix chinensis and Salix matsudana. The DCCA axis 1, explained 59% of variance of species and environment relation and showed significant relationships to 4 base cations, reflected the gradient of 4 base cations, which meant they all influenced plant distribution. While Ca²⁺, owned longest axis and smallest angle, was the most important factors. The DCCA axis 2, explained 25% of variance of species and environment relation, reflected the gradient of Mg²⁺ and K⁺. And we found the number of plant species decreased with the increasing of both DCCA axis 1 and DCCA axis 2. With the decreasing of base cations concentrations of plots, the values of diversity indices, both Shannon-Wiener index (H') and Simpson index (DS), increased. Moreover, significantly relationships were found between 4 base cations concentrations and H', DS (P<0.05). Hereafter, only Ca²⁺ was selected through stepwise regression, which indicated the importance of Ca²⁺ on plant diversity. The results may mean that calcium ion, with highest concentration on the beach, had most important effect on plant distribution and diversity in Hangzhou Bay coastal wetlands, which is different to other beach wetlands in China.