The invention relates to an unpowered rainwater collection and timing irrigation device for roof greening. For an existing commonly-used mode of achieving water catchment at the roof top of a building, timed and quantitative automatic irrigation function on plants cannot be achieved, only the water resource problem is solved, and unmanned management is not achieved. The unpowered rainwater collection and timing irrigation device for the roof greening is characterized by comprising a rainwater collector, a water collection tank, a floating water controller and a drip pipe system which are installed in sequence from top to bottom, wherein a lower water outlet of the rainwater collector extends into the water collection tank, a water inlet hole is formed in the upper portion of the water collection tank, a drainage opening is formed in the lower portion of the water collection tank, and overflow openings are formed in the edges of the upper side portion of the water collection tank; the floating water controller is of a test-tube-shaped structure with an upward opening, the floating water controller is invertedly buckled below a water outlet hole of the rainwater collector, the floating water controller is up and down adjusted according to the buoyancy subjected in the water collection tank, and the floating water controller can block the drainage opening of the water collecting tank when the floating water controller sinks; the drip pipe system is located at the bottom of the water collecting tank and connected with the drainage opening formed in the bottom of the water collection tank. The unpowered rainwater collection and timing irrigation device for the roof greening has the advantages that the technical purposes of rainwater collection and timing irrigation device for the roof greening are achieved, the structure is simple, and implementation is convenient.