The invention discloses a hydrogen chloride (HCl) oxidizing reaction process and HCl oxidizing reaction system based on series-connected fluidized bed and thermal insulating fixed bed. The reaction process comprises the following steps: evenly mixing hydrogen chloride with oxygen, carrying out an oxidizing reaction of the mixed gas in a fluidized bed reactor, performing heat exchange after the mixed reactant gas leaves the fluidized bed reactor, reducing the temperature of the reactant mixed gas to the temperature range of 350-410 DEG C, and then carrying out further oxidizing reaction in an thermal insulating fixed bed reactor connected in series with the fluidized bed reactor, wherein the conversion rate of the hydrogen chloride in the fluidized bed reactor is 30%-70%; the reactant mixed gas after reacting in the fluidized bed reactor enters the fixed bed reactor to have a heat insulated reaction, and finally, the highest conversion rate of the hydrogen chloride reaches 92.1%.