Abstract: Marine microplastic pollution has become one of the highly concerned global environmental issues. In this study, microplastic pollution in tidal flats seawater and rivers of Sishili bay were investigated along the coastal zone of the North Yellow Sea. The average abundance of microplastics in the surface water, river and tidal flat were （5.2±1.6） N/L, 5.2 N/L and （163.2±151.3） N/kg (d.w.), respectively. The fibers were dominated in microplastic types, which was primarily from aquaculture farming and river inputs, followed by fragments, films, foams and particles. The majority size of microplastics was < 1 mm (>50%). The distribution of microplastics in the water and tidal flat of Sishili bay showed significant spatial differences, which are mainly affected by aquaculture farming, daily living and hydrodynamics. More data are required in the future to understand the mechanism of microplastics distribution in the coastal open bay.