In seasonal frozen soil area, in order to study the unconfined compressive strength of cemented soil modified with red mud and steel slag after freezing-thawing cycles and the influence of steel slag and red mud, after the addition of different content of red mud and steel slag to cemented soil, unconfined compressive strength and scanning electron microscopy(SEM) tests were conducted after different freezing-thawing cycles. Results show that: when the red mud content is 8% and steel slag content is 2%, the unconfined compressive strength of cemented soil is largest and less affected by freezing-thawing cycle; the unconfined compressive strength of modified cemented soil decreases with freezing-thawing cycles. Besides, the first freezing-thawing cycle has the strongest influence on the modified cemented soil. From the SEM experiment, it is concluded that adding red mud and steel slag is helpful to increase AFt crystal and C-S-H gel hydration products in the cemented soil, the strength improvement mechanism of modified cemented soil and the damage mechanism in the condition of freeze-thaw cycle were thus elucidated.