Abstract: Considering the intertidal belt in the estuary and coastal sea area,a variable boundary mass transport model is needed. In this paper,based on the established ECOM model,a variable boundary particle tracer model is developed,and is applied in Jiaonan sea area. This paper discusses the transfer character of the particle forced by M2 tide in 3-D space. This model can be applied to the management of the marine environment in the estuary and coastal sea area.