The invention discloses a chemical and phase-transition compound cooling device and a method, comprising a working medium tank, a power pump, a closed container and a nozzle, wherein the working medium tank is connected with the power pump by a pipeline; the power pump is connected with the nozzle by a pipeline; a mixed working medium formed by carbon dioxide hydrate and carbon is stored in the working medium tank; the carbon dioxide hydrate and carbon are mixed with each other in a mol ratio of 1:54-65; the nozzle is arranged at the inner top end of the hollow chamber of the closed container; a heat sink is arranged at the bottom of the closed container; an outlet is arranged at the upper end of the closed container; and the working medium tank is made of temperature-preserving heat-insulating pressure-withstanding material. The method comprises the following steps of spraying the mixed working medium of the cooling system on the surface of the heat sink; firstly absorbing heat and gasifying the carbon dioxide hydrate so as to generate carbon dioxide and vapor; secondly leading the carbon, the carbon dioxide and the vapor to generate chemical endothermic reaction so as to quicklyremove a large amount of heat. In the system, the spraying and cooling technology is combined with the chemical endothermic reaction technology, thus achieving the aim of quickly dissipating the heatof high-power elements.