The invention discloses a method for enhancing the biological denitrogenation effect of constructed wetland. According to the invention, a carbon source slow-release apparatus is arranged at a front end of the constructed wetland, sewage passes through the carbon source slow-release apparatus, and then is introduced into the constructed wetland; the external part of the carbon source slow-release apparatus is formed by a netted framework structure, and the agricultural waste is provided in the internal part of the carbon source slow-release apparatus. The agricultural waste is placed at the front end of the constructed wetland, by controlling the adding rate of the agricultural waste and blending ratio, the slow release effect of the agricultural waste is used for providing a carbon source for denitrification and nitrogen removal for the constructed wetland, so that the total nitrogen removing rate of the constructed wetland is increased.