[Objective] To analyze the physicochemical properties of the cotton and peanut biochar, and investigate the effects of rainfall on Cu(Ⅱ) leaching quantity under simulated rainfall in natural conditions in order to assess the feasibility of using straw biochars to remediate the Cu(Ⅱ) contaminated soil.[Methods] Cotton and peanut straw was selected as raw materials to produce biochar by using limited oxygen pyrolysis method under 350, 500 and 650℃ conditions. A laboratory simulation test was used to analyze the effects of different biochar amendment on soil buffering capability and the retention capacity of heavy metals. Biochar with 1% carbon/soil dry weight ratio were supplied in Cu(Ⅱ) (200 mg/kg) contaminated brown soil.[Results] The ratio of O/C and H/C in two different kinds of biochar were decreased gradually with the increase of temperature, while the BET surface area of biochar was decreased with the increase of temperature. The pH value of soil leaching solution in biochar added soil was significantly higher than that of the control treatment, and the effect of peanut biochar was more significant. With the increase of leaching times, Cu(Ⅱ) leaching amount in biochar added soil was significantly lower than that in the control treatment. The peanut biochar addition could increase the specific adsorptions of Cu(Ⅱ) in soil, especially at 650℃ condition.[Conclusion] Both of the two straw biochar addition significantly improve the soil buffering capability and the retention capacity of heavy metals in soil, in which the effect of peanut biochar is more obvious.