An intravenous infusion system with real-time infusion rate monitoring and closed-loop infusion rate control is disclosed. The intravenous infusion system comprises: an infusion module, providing drug solution through an intravenous catheter; a flow sensor module, installed around an outer periphery of the intravenous catheter, transmitting ultrasounds to the intravenous catheter and receiving ultrasounds reflected or penetrated therefrom to determine a real-time volumetric flow rate of the drug solution in the intravenous catheter, and converting the real-time volumetric flow rate into a flow rate electronic signal; and a communicating module, electrically and signally connected with the flow sensor module, receiving the flow rate electronic signal and delivering the flow rate electronic signal to an external agent connected thereto.