In order to understand the adaptability of porous fiber cotton in the drainage (storage) layer of a green roof, plastic concave-convex drainage plates and porous fiber cotton were respectively used as drainage (storage) layers of green roof test device, and the differences between porous fiber cotton and traditional drainage (storage) layer materials were explored through monitoring runoff, water quality, and plant growth in rainfall simulation test. The results show that, compared with plastic concave-convex drainage plate, porous fiber cotton with a thickness of 2 to 8cm is more suitable for the drainage (storage) layer of green roof, which can sustain plant growth during dry periods, improve stormwater retention effect and suspended solid reduction effect during rainfall periods, and reduce the leaching of TP and CODCr, but it will aggravate the leaching of TN.