Abstract: Arsenic has the chemical nature and toxicity to environment like heavy metals, and its toxicity will have a serious impact on human health, animal or plant.Only 0.1 g arsenic trioxide can cause human death, and long-term excessively drinking water or eating other foods containing arsenic will cause cancer in human organs.To reduce the effect of arsenic on human body, animal and plant, this paper uses unmodified biochar and biochar modified by FeCl3?6H2O as test material; the former was prepared using cotton stalks whose carbonization temperature and time were 500 ℃ and 4 h, respectively, and the latter was prepared with the 20∶1 mass ratio of cotton stalk biochar to FeCl3?6H2O.A total of 35 groups of soil containing unmodified biochar or modified biochar or arsenic were designed, and the arsenic content of cabbage that was planted in pot was tested by atomic fluorescence spectrometer (PF6-1) to explore the influence of unmodified biochar and modified biochar on soil and plants absorbing arsenic.The results showed that: Unmodified biochar (10-40 g/kg) or modified biochar (10 g/kg) could promote the growth of cabbage, and the biomass of cabbage was the largest when the unmodified biochar was 20 g/kg and the modified biochar as 10 g/kg, which was 8.26 and 6.68 g per pot respectively.When the content of modified biochar was 10 g/kg, the biomass of cabbage was bigger than the control group and the treatment group with equivalent amount of unmodified biochar.The arsenic in soil was mainly residual form, and soluble arsenic increased by 0.22%-3.36% and 0.96%-3.70% respectively when the arsenic content was 10 and 20 mg/kg and the addition content of biochar was 10-40 g/kg.The soluble arsenic had no effect when the arsenic content was 10 mg/kg and the addition content of modified biochar was 10-40 g/kg, but the soluble arsenic decreased by 0.12%-0.58% when the arsenic content was 20 mg/kg.The content of soluble arsenic was increasing with soil arsenic content increasing when the content of arsenic in soil was 40 and 80 mg/kg; after adding biochar (10-40 g/kg), soluble arsenic increased by 0.21%-1.56% and 2.11%-8.94%, respectively, but the form of arsenic was mainly aluminum arsenic, and arsenic residues followed.The variation of arsenic mass fraction in edible parts and roots of cabbage in each treatment group was different after adding biochar (10-40 g/kg), but the mass fraction of arsenic in edible parts of cabbage significantly reduced from 18.28 to 2.66 mg/kg (P<0.05), and the mass fraction of arsenic in roots of cabbage significantly reduced from 133.99 to 20.21 mg/kg (P<0.05) after adding same amount of modified biochar.Comparing the modified biochar and unmodified biochar, it was found that modified biochar could reduce the content of soluble arsenic in soil and inhibit cabbage from absorbing arsenic.Therefore, this study may provide data support and theoretical basis for the application of modified biochar and unmodified biochar in soil restoration.