<p>Phosphoric acid-based geopolymer owns a great solidification/stabilization (S/S) effect on acidic Pb²⁺ contaminated soil, especially the modified phosphoric-based geopolymer (named MAPG) synthesized from fly ash, metakaolin and aluminum dihydrogen phosphate. Nevertheless, the long-term S/S performance of MAPG on the acidic Pb²⁺ contaminated soil subjected to freeze–thaw (F–T) cycles is not yet investigated. In this article, the long-term S/S performance of MAPG stabilized acidic lead contaminated soil subjected to F–T cycles through many test methods was studied, and a long-term stability evaluation model based on the resistivity index ρ was proposed to reflect the degradation performance of MAPG stabilized acidic Pb²⁺ contaminated soil subjected to F–T cycles. The results show that the F–T cycles could destroy the stabilized soil structure, causing a mechanical diminution of the stabilized contaminated soil, but the compressive strength still met the strength standard (&gt; 0.35&#xa0;MPa) after 8 F–T cycles. The stabilized contaminated soil resistivity firstly declined rapidly under 0–4 F–T cycles and then stabilized after 4 F–T cycles. In deionized water, acetic acid and sulfuric acid-nitric acid environments, the MAPG binder had good S/S impact on acidic Pb²⁺ contaminated soil subjected to F–T cycles, but when the binder dosage was 6%, the Pb²⁺ leaching after F–T cycle exceeded 5&#xa0;mg/L (hazardous waste leaching toxicity limit) for the stabilized soil under acetic acid environment. According to the established evaluation model, the service time of MAPG binder stabilized acidic Pb²⁺ contaminated soil in typical F–T region could reach 100&#xa0;years. The stabilized contaminated soil pH decreased with a rising F–T cycles times, while electrical conductivity rowed with the raising F–T cycles times with a good relevance. Lead phosphate compounds and berlinite were found in the MAPG stabilized contaminated soil, and F–T cycles could induce the microstructure damage of stabilized contaminated soil.</p>