In Hokkaido, where peatlands are widely distributed, Picea glehnii forest on the peatland is one of the representative components of a wetland landscape. The dynamics of the forest have been suggested to be affected by the gradient of water environment, but it has still not been demonstrated. In this study, we examined possible changes in stand structure of the peatland Picea glehnii forest in relation to the distance from a major water channel. Our study site is located in the Dorokawa basin, with completely flat topography, in northern Hokkaido. We set up circle plots in the five locations (three repetitions for each), which represent the distance from the Dorokawa river, a major water channel. In 2011, we conducted tree census, followed by tree baller sampling and vegetation survey. The environmental conditions were also measured in the growing season. The results showed the difference among the locations in water table, as well as soil pH and canopy openness. We also found clear changes in vegetation as well as the growth rate of overstory trees. The seedlings of Picea glehnii are distributed almost in the wettest location. The relationships of the distance or the environmental measures with those stand properties will be discussed.