Biochar is a kind of highly aromatic carbonized material produced through thermal decomposition of biomass under reductive conditions (i.e. in the absence of or with a limited supply of oxygen). Biochar is found to be able to play an important role in mitigating global climate change, removing pollutants from water and soil, as well as maintaining functions of ecosystems. During the pyrolytic processes of biological materials, a certain amount of organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), would form and remain on the surface of the biochar. Consequently, increasing application of biochar may bring about a certain risk to the environment. Current researches pay much attention to the positive effects biochar may have, while ignoring its potential hazards to the ecosystem. To assess environmental risk of the PAHs in biochar, it is necessary to determine the contents of total and bioavailable PAHs in biochar. At present, the following four methods, i.e. Soxhlet extraction, accelerated solvent extraction (ASE),ultrasonication extraction and thermal extraction, are available for determining total PAHs in biochar. However, the four methods were often used to determine semivolatile organic compounds in solid matrix (soil or sediment). Among the four methods, the Soxhlet extraction and ASE methods are the most commonly used ones, because of their higher recoveries of target compounds. However, when they are used to extract PAHs in biochar, PAHs recoveries depend highly on solvents and the biochar per se. In the case of determining bioavailable PAHs, limited information is available besides the polyoxymethylene (POM) passive sampling method. Altough PAHs in biochar are formed mainly through two pathways, i.e. low temperature pyrolysis (< 500℃) and high temperature pyrolysis (> 500℃),the formation process is still very complicated, because there are a lot of factors that affect yield and composition of PAHs in biochar, including feedstock resource, pyrolysis temperature, heating rate, holding time, etc. With the respect of feedstock, little information is available concerning relationship between content of lignin and/or cellulose and PAHs in biochar. As regards pyrolysis temperature, biochar out of low-temperature pyrolysis generally contains more low-molecule-weight/high-vapor-pressure PAHs, whereas biochar out of high-temperature pyrolysis contains more high-molecule-weight /lower-vapor-pressure PAHs. However, the relationship between temperature and PAHs yield is still controversial. Heating rate and holding time of the pyrolysis are two important factors influencing PAHs yield in biochar. Generally speaking, during the process of slow pyrolysis with long holding time, PAHs are more likely to escape into the atmosphere as gas whereas during the process of fast pyrolysis, they are more likely to get condensed and adsorbed onto the surface of biochar. The other factors that influence PAHs content in biochar include ash content and moisture content of the feedstock, and presence of oxygen during the process of pyrolysis or the post-pyrolysis cooling process. Researches demonstrate that feedstock is high in ash and moisture content plus presence of a little oxygen facilitates formation of more PAHs in biochar.