The invention provides a rotary electrostatic generator, which comprises a power collecting component, a stator, a stator supporting member, a rotor, a rotor supporting member, a rotating shaft and a bearing, wherein the power collecting component is fixed on the rotating shaft, the rotating shaft, the rotor supporting member fixed on the rotating shaft and the rotor connected to the rotor supporting member are driven to rotate together by an external force, the rotor and the stator are enabled to be contacted with or separated from each other periodically, relative sliding friction is generated between a first friction layer and a second friction layer on the contact surface, and the friction area is changed, thereby being capable of generating electric signals and outputting the electric signals to an external circuit. The electric signal output not only can act as a power supply to drive electronic devices such as an LED, an LCD and the like or charge energy storage devices such as a lithium battery, a capacitor and the like, but also can be used for detecting the flow rate of a fluid in real time.