In order to investigate the relationship between some properties of coal-based humic acids and arsenic availability in soil, and potential utilization and application direction of coal-based humic in the remediation and improvement of arsenic contaminated soil, a pot experiment was conducted to study the effects of four coal-based?humic acids on the content and speciation of arsenic in soil, the growth of pakchoi (Brassica campestris L. ssp.), and the adsorption and distribution of Arsenic in pakchoi. The results showed that No. 6 and No. 10 coal-based humic acids significantly reduced the contents of exchangeable Arsenic and carbonate bound arsenic, thus the content of available arsenic in soil was reduced significantly, meanwhile, the transfer and accumulation of arsenic from underground part to aboveground part of pakchoi were inhibited. The contents of exchangeable arsenic and available arsenic in soil and the total amount of arsenic in aboveground part of pakchoi in No. 10 coal-based humic acid treatment reduced 49.18%, 42.22%, and 15.17% than those in arsenic treatment, respectively. However, No. 9 and No. 11 coal-based humic acids increased the contents of exchangeable arsenic and carbonate bound arsenic, and significantly increased available arsenic in soil, and promoted the arsenic absorption, the transfer of arsenic from underground part to aboveground part of pakchoi. The contents of exchangeable arsenic and available arsenic in soil and the total amount of arsenic in aboveground part of pakchoi in No. 9 and No. 11 coal-based humic acids treatments increased 10.58% and 5.95%, 31.11% and 22.22%, 20.81% and 17.21% than those in arsenic treatment, respectively. The four coal-based humic acids all promoted the growth of pakchoi, and the promotive effect followed the order of No. 10＞No. 6＞No. 11＞No. 9. In conclusion, No. 6 and No. 10 coal-based humic acids, which had lower E4/E6 values, larger molecular weights, and lower contents of total acid base, had obviously inactivate effect on arsenic in soil, and could be used to control the arsenic absorption of crops and inhibit the transfer of arsenic from underground part to aboveground part of crops in mild arsenic polluted soil, so as to ensure crop safety production. No. 9 and No. 11 coal-based humic acids, which had larger E4/E6 values, lower molecular weights, and larger contents of total acid base, promoted arsenic activity and could be used as activator in moderate and severe arsenic polluted soil to strengthen phytoremediation.