Tiangou and eaves ditch are the last part of rainwater flow, which are frequently washed by water flow and easy to accumulate water. Moreover, the structure of Tiangou and eaves ditch is thin, the deformation is large, the Yin and Yang angles are many, and the base surface is not even. Therefore, the principles of multi-channel fortification, additional reinforcement and joint sealing should be followed. Firstly, additional reinforcement layers with different thickness requirements are made at rainwater outlet, Yinyang angle, whole ditch bottom and side. Because of the large turning angles of the base of the gutter and eaves, it is advisable to use film to strengthen the roof. The space-laying method should be adopted at the junction of the roof and gutter. The width of the space-laying is not less than 200 mm, and the end of the film should be coated with paint or sealed with sealing materials. For example, when coiled materials are used in Tiangou and eaves ditch, it is advisable to lay along ditches, reduce lap joints, improve construction reliability, and turn over from the bottom of ditches to the top of eaves. The end of coiled materials is fixed with cement nails and sealed with sealing materials. If the roof is a rigid fine stone concrete waterproof layer, the groove should be left at the junction with eaves and gutters, and the sealing material should be filled in.