The present invention discloses a method and system for thermal desorption treatment of organic-contaminated soil and treatment of desorbed waste gas. The system includes a thermal incinerator, a desorption flue gas temperature regulating device, a thermal desorption reactor, a dust collector, a heat exchange/steam separator, an absorption reactor, a star-shaped unloader, and a soil cooler. An absorbent containing organic pollutants is used as a fuel, and subjected to thermal incineration to achieve the decomposition and harmless treatment of the organic pollutants; and high temperature flue gas generated by the incineration is used as a heat carrier for thermal desorption remediation of the organic-contaminated soil; and by means of the high solubility capability of fuel oil to organic matter, the fuel oil is used as an absorbent to absorb and purify the organic pollutants in desorbed waste gas, so that the gas is purified gas and up-to-standard discharge is achieved. The present invention achieves the thermal desorption of the organic pollutants, the absorption and purification of the pollutants in the desorbed waste gas, and the thorough decomposition of the organic pollutants; the fuel oil has both functions of the absorbent and the fuel, and the present invention has the advantages of short process, low energy consumption, simple equipment and low cost.