Abstract: It has been disputed whether eitrate-biearbonate-dithionite (CBD) can distinguish between lithegenie and pedogenie iron oxides or can solve coarse particles of iron oxide. Therefore, we used CBD technique to make an experiment on the extracted amount of different coarse particles (>63 μm) of iron oxide that vary with time at the room temperature and heated conditions. The results show that CBD technique can dissolve coarse particles (>63 μm) of iron oxide in the room conditions, and hematite was dissolved most quickly,the largerst dissolved amount came from goethite and the lowest dissolved rate was showed by magnetite. Meanwhile, the dissolved amount of all iron oxides went higher in the heated conditions. Pyrite was calcined at 400℃ and 500℃ and formed hematite,and their amounts reached the maximum in the same conditions, indicating that the smaller, the grain size,the larger,the dissolved amount.