Abstract:The effect of freeze/thawing cycling on the soil iron oxide and its activity were analyzed through artificially controlling temperature and indoor simulation. The black soil of various water contents (10%, 40%, 70%, 100% and 120% of the field capacity) collected from the northeast China, was frozen at -30℃ for 24 h, then thawed at 20℃ for 24 h, which is one freeze/thawing cycle, and the soil samples were subsequently refrozen and thawed for 0, 1, 3, 6, 9 times. The results showed that freeze/thawing cycling affected the soil free iron oxide (Fef), amorphous iron oxide (Fea) and the crystal iron oxide (Fef -Fea) significantly at 0.01 level. With the freeze/thawing cycling increasing, the content of the Fef and the Fef?-Fea decreased firstly, than increased, the content of the Fea presented fluctuant change. The amorphous iron oxide was a good indicator of the iron oxide under different freeze/thawing cycling for its stronger sensitivity. The effect of the freeze/thawing cycling on the iron oxide activity and (Fef?-Fea)/ Fea was significantly, and the iron oxide and (Fef?-Fea)/ Fea presented fluctuant change with the freeze/thawing cycling.