For the in situ reduction of landfill sludge, the reduction effect of freeze-thaw process combined with vacuum preloading was studied. Samples were taken from a landfill in Shanghai. First, five freezing temperatures (0, -6, -11, -14.5, and -18.5 ℃) were set during the freeze-thaw treatment of sludge to analyze the effects of freezing temperature on specific resistance of sludge and critical water content. Then, a model test was conducted to investigate the variation of displacement, dewatering rate, settlement, volume reduction ratio, water content, and unconfined compressive strength under different working conditions by comparing single vacuum preloading with freeze-thaw treatment combined with vacuum preloading. Results show that the freeze-thaw treatment could effectively reduce the specific resistance of sludge and improve its dehydration performance, and the optimum freezing temperature was -11 ℃. The sludge after freeze-thaw treatment showed a good drainage consolidation effect in the process of vacuum preloading, and the optimum treatment temperature was consistent with the results of sludge specific resistance test. The minimum water content of the treated sludge reached 54.0%, the unconfined compressive strength was up to 42.84 kPa, and the maximum reduction ratio was 40%, which achieved the purpose of sludge reduction.