Through processing different soil acidification treatments , then using ferron colorimetric method, we evaluate two different forms of soil iron oxides under the two conditions of different acidification degree and different acidification time intending to find out the effect of acidification to the morphology transformation of iron oxide in the soil. The results show that there are many forms of iron oxides in soil. With the increase of oxide soaking days, the content of free iron oxide and amorphous iron oxide in soil generally presents the opposite change tendency. The content of free iron in ninth day is significantly higher than other days.While the content of amorphous iron oxide in sixth day is significantly higher than in ninth day. When pH value are 3.6 and 4.5,the content of free iron oxide in soil shows no difference between each other under the different fertilizer treatments, so is the content of amorphous iron oxide when pH value are 4.5 and 5.6.