Biochar is widely used to passivate the heavy mentals-contaminated soils, but aging process may affect the passivation effect on soil heavy metals. This study designed a compound aging method which containing simulated acid rain, dry-wet alternation, freeze-thaw cycles, root exudates, fertilizer application and other factors, and the effects of soil pH, water extractable, CaCl2 extractable and chemical fractions of cadmium in soil treated by the two kinds of straw biochars (JN and HR) were investigated before and after aging. The results showed that: the pH of JN and HR were 9.06 and 8.84, respectively, and their specific surface areas are 5.96 m2/g and 7.06 m2/g, respectively, and rich organic functional groups. Before aging, JN and HR increased soil pH by 0.21 and 0.29 units. Compared with CK, JN and HR treatment reduced CaCl? extractable cadmium by 54.5% and 59.1%, but water extractable cadmium did not significantly change. After compound aging, the soil pH in each treatment group decreased significantly by 3.38 ~ 3.59 units, and the water extractable cadmium in JN and HR treatment was 2.44 ~ 6.59 times higher than that of CK. The CaCl2 extractable cadmium for all soils after aged for one year was 2.03 ~ 4.13 times higher than that before aging. Aging treatment reduced the acid soluble cadmium for all soils and transformed it into the reducible fraction. Due to the continuous addition of root exudates, the oxidizable cadmium increased with aging time, and CK, JN and HR increased by 30.7%, 39.2% and 46.5% respectively after two years. In conclusion, the addition of root exudates in this study quickly reduced the soil pH to a very low level, significantly reduced the acid-soluble cadmium content and increased the oxidizable cadmium content. In future, it is necessary to design an aging method closer to the real environment and evaluate the long-term passivation effect of biochar on soil cadmium.