Wetland is a hotpoint which is paid a close attention to by many the scientists in different subjects, but wetland researches are very young and under developing. This paper discussed some basic issues of wetland researches and show that: wetland could be described as a physical synthesis which composed of water, soil and vegetation and the process is dominated by that of water in the surface layer of the earth. The main scientific issue is the filtrationism which could defined as the movement, transference, redistribution and effects of water, nutrients and contaminants in multi interface through terrestrial and aquatic interaction in wetland, which is the core of ecological process and function in wetland. It includes water process and effects, cycling process and effects of nutrients and contaminants, wetland productivity and biodiversity and so on. The frame of wetland sciences system and the priority in wetland researches in China were also proposed.