P. vittata is one of the hyperaccumulators of arsenic (As), a series of experiments were conducted in a horizontal tube furnace to study the transformation behavior of As during the thermal treatments of P. vittata in different atmospheres (air, N₂, CO₂). As release exhibited similar tend in different atmospheres during the temperature ranged from 400℃ to 800℃. It increased firstly due to the volatility of inorganic As, and then dropped probably because of the self-retention of As by alkali and alkali earth metal enriched in this P. Vittata. The As release reached the peak value (43%) at 500℃ during combustion (in air), while the temperature was 600℃ when the peak value (60%) occurred both during pyrolysis (in N₂) and gasification (in CO₂). When the temperature exceeded 800℃, the As release decreased continuously during combustion while it increased rapidly to 90% during pyrolysis and gasification, which could be due to the falling of thermal stability of inorganic As compounds in reducing atmosphere. The results of simulation by FactSage showed that the main form of As in different atmospheres was different with increasing the temperature. The main form of As during combustion was Ca₃(AsO₄)₂(s), while it was elemental As(g) and AsN(g) during pyrolysis and gasification, respectively. Moreover, the results of As transformation simulation were in accordance with the experimental results overall.