The invention relates to a heat radiation system of a server. The heat radiation system comprises a cooling device, a heat radiating groove for accommodating a refrigerant, a heating element and a heat exchanger. The heating element arranged in the heat radiating groove is immersed by the refrigerant and is used for transforming the refrigerant into refrigerant steam; and the heat exchanger is used for obtaining the refrigerant steam in the heat radiating groove. Moreover, the heat exchanger obtains the refrigerant steam, carries out heat exchanging on thermal fluid generated by the refrigerant steam and the cooling device, and carries out natural cooling, so that the refrigerant steam is condensed into cold fluid and the cold fluid returns to the heat radiating groove. With the heat radiation system, working performances of all assemblies can be protected from being affected by the temperature; and the internal space of the heat radiating groove can be saved.