Rainwater pipe system suitable to be used on existing building energy-saving modification engineering

The utility model discloses a rainwater pipe system suitable to be used on existing building energy-saving modification engineering for rainwater drainage on the roof of a building with an external heat preservation layer. The rainwater pipe system comprises an elephant trunk which is used in the original building and is retained at a position penetrating through a parapet wall and a water articulated chute and a rainwater funnel which are dismounted from the original building and are rearranged on the rear wall surface of the added heat preservation layer. The improvement is that a transitional connection plate is arranged at an outlet of the elephant trunk and the rainwater funnel; a T-shaped hole for inserting the elephant trunk and horizontally inputting part of the rainwater funnel is formed in the transitional connection plate; the surface of the lower side of the hole is downwards inclined to form a downstream slope relative to the wall surface from inside to outside; the rainwater funnel is arranged i