Abstract: Heavy metals contaminated soils pose a serious risk to human beings and animals via direct exposure and food chain. Biochar, a carbon-rich material, is used to remediate heavy metals contaminated farmland. This strategy provides an effective method for utilizing biomass resources and ensuring food safety. With increasing attention, the number of published articles concerning biochar has been increasing in the recent ten years, therefore providing researchers with a large amount of evidence and insights. In this study, the latest studies of biochar in the remediation of heavy metals contaminated farmland were reviewed, with the focus on possible mechanisms of biochar-heavy-metal interactions, related impact factors, and in-situ application of biochar at the field scale. Biochar showed a strong sorption ability, attributed to its physiochemical properties such as large specific surface area, abundant functional groups and high cation exchange capacity. The application effect of biochar was greatly influenced by its characteristics. After summarizing biochar's physiochemical property data in recent years, the study discussed the changing law of biochar's properties with the alteration of feedstocks and pyrolysis temperature, respectively. To modulate the properties of biochar for soil remediation, various modifiers with different concentrations were adopted, including acids, bases, oxidizing agents, organic solvents and metal salts or oxidizing agents. In general, the purposes of modification were to enlarge the surface area, to change the functional groups, and to increase the adsorption performance and catalytic capacity. Furthermore, the immobilization mechanisms of heavy metals by biochar were illustrated. The direct immobilization could be achieved through physical absorption, electrostatic attraction, ion exchange, complexation, precipitation, and redox reaction. Besides, the indirect effects of biochar on heavy-metal mobility and bioavailability, which could be achieved via impacting soil characteristics and thus heavy-metal-soil complexation, were less understood and could be largely underestimated. Biochar addition could alter many soil properties including pH value, dissolved organic carbon, mineral composition, and cation exchange capacity. These changes would affect heavy-metal-soil interactions and thus heavy-metal mobility and bioavailability. Many laboratory studies had demonstrated biochar's effectiveness in decreasing the bioavailability of heavy metals as well as improving soil quality. However, the value of biochar in the remediation of contaminated land had not been well tested in the field. In different field trials, distinct results (beneficial, neutral or adverse effects) had been reported due to wide variations in field conditions and biochar characteristics. To better understand whether biochar application could provide a promising direction for soil remediation, this review was undertaken to assess the published field trial. The results of most previous field trials indicated that biochar could potentially reduce heavy-metal bioavailability in the field. Meanwhile, a significant decrease in the heavy-metal enrichment of the crops was observed. It was found that the use of biochar may help increase crop yields on polluted farmland and reduce the amount of mineral fertilizer used in the field. The application of biochar could inactivate heavy metals through improving soil physicochemical properties (pH, cation exchange capacity, water retention capacity etc.). In addition, it also could be used to enhance the uptake of soil nutrients for plant growth. However, according to a majority of studies, biochar's effectiveness in reducing the impacts of heavy metals depended on a myriad of factors in the field, including biochar applying process (variety and dosage rate of the biochar, mixing depth), agronomic measure (nitrogen-phosphorus-potassium fertilizer application) and climatic conditions (air temperature and precipitation). In the last part, future research on the perfection of the mechanisms of soil remediation using biochar, the expansion of the scale, and the long-term monitoring on soil was prospected.