To investigate the process of pollutant transport in sinuous open channel flow, a 3D hydrodynamic-pollutant coupled large-eddy simulation model was established according to the scalar tracer experiment. The influence of different release positions in transverse and vertical directions of point source on the concentration distribution in the downstream was analyzed. The results show that the streamwise velocity, vorticity and turbulent kinetic energy have clear relations and the secondary currents exert dominant impact on transport and mixing. Besides, the variance in transverse and vertical position of point source has significant influence on mixing efficiency and spatial distribution of pollutant. Specifically, the point source placed near the center of cross section in transverse direction or near the bottom of channel in vertical direction will result in a higher mixing efficiency and a wider influence range. There exists a positive correlation relationship between mixing rate and distribution range in the near field. The variance of point source position in a sinuous open channel mainly influences the pollutant’s mixing within a single period.