The invention discloses a natural circulating tank type solar heat collecting system. In the system, a condensing downcomer is connected with an S-shaped bent pipe, a first pipeline rotary connecting valve, a flow control regulating valve, a heat collecting pipe, a metal connecting pipe, a main steam pipe, a second pipeline rotary connecting valve, an ascending tube and a steam heat exchanger in sequence through corrugated connecting pipes; a vacuum extract port is arranged on the tail end of the ascending tube; a hydraulic system, a reflector bracket and a bracket support are connected with a rotating shaft respectively; a reflector surface is arranged on the reflector bracket; the heat collecting pipe and a light intensity sensor are connected with the reflector bracket through a heat collecting pipe support; the first pipeline rotary connecting valve, the second pipeline rotary connecting valve and the S-shaped bent pipe are connected with a pipeline rotating pedestal support, and are then coaxially fixed on the bracket support with the rotating shaft; a rotary pipeline top support is fixed on the end of the reflector bracket; the steam heat exchanger is arranged on an iron tower; and the system is controlled by a control system. By introducing natural circulation and adopting efficient and novel connection and control mode, the system efficiency and stability can be improved.