The invention provides a heat dissipation system of a data center machine room. The heat dissipation system comprises heat collection modules, a gas-liquid separator, a liquid storage tank, a heat dissipation device and a fluid working medium, wherein the heat collection module, the gas-liquid separator, the liquid storage tank and the heat dissipation device form a heat dissipation circulating pipeline, the fluid working medium flows in the heat dissipation circulating pipeline, and the collection module comprises an evaporation section, a fluid inlet pipeline, a fluid outlet pipeline, a control mechanism, an induction mechanism and a steam branch pipeline. According to the invention, the data center machine room automatically switches the heat dissipation mode and the working mode to take away the heat generated by the evaporation end of the heat collection module according to the outdoor temperature condition and the thermal load condition of the machine room by taking energy consumption minimization as a target during operating; the flow is automatically adjusted through the flow self-strain mechanism of the heat collection module so as to solve the problem of heat production difference between the heat collection modules in the cabinet; and the refrigeration cycle, the gravity-driven self-cycle and the pump-driven two-phase flow cycle share a radiator array.