The invention discloses an activating agent used for food heating agent. The activating agent is prepared from sodium sulfate, sodium chloride, sodium peroxide, an anti-freezing agent and water, wherein the content of sodium sulfate is 3% to 8%, the content of sodium chloride is 5% to 10%, the content of sodium peroxide is 1% to 5%, the content of the anti-freezing agent is 3% to 8%, and the content of the water is 70% to 85%. According to the activating agent, an electrolyte is separated from the formula of the heating agent, the quality guarantee period of the heating agent can be prolonged to 36 months from 18 months, and the anti-freezing agent can enable the heating agent to be started at low temperature.