Recovery of aluminum from secondary aluminum dross by roasting with ammonium sulfate and leaching with water is one of the most important methods to harmlessly utilizing secondary aluminum dross. However, fluoride leaching toxicity of the leaching residue should satisfy the national standard's prescription (the mass concentration of inorganic fluoride is less than 100 mg/L). Thus, it is necessary to study the F migration in the Al extraction process of roasting secondary aluminum dross with ammonium sulfate and leaching with water. In this work, the regularities about migration and transformation of F in the process of extracting Al from secondary aluminum dross via roasting with ammonium sulfate and leaching with water was investigated by fluoride ion electrode, XRD, XPS, SEM and XRF. The results showed that prolonging the roasting time, elevating the roasting temperature and increasing the mass ratio of ammonium sulfate to secondary aluminum dross could accelerate the migration of F from secondary aluminum dross to roasting off-gas. Additionally, extending the leaching time, increasing the leaching temperature and increasing the liquid-to-solid ratio was beneficial to reduce the content and proportion of F in the leaching residue. About 43.85% of F released from secondary aluminum dross to roasting off-gas in the form of gas, 23.92% of F went into the leaching solution as fluorine ion, and 32.23% of F remained in the leaching residue in the forms of AlF3 and AlF3?3H2O under the most suitable conditions with the roasting temperature of 450℃, the roasting time of 2 h, the mass ratio of ammonium sulfate to secondary aluminum dross of 6:1, the leaching temperature of 85℃, the leaching time of 80 min, and the liquid-to-solid ratio of 6:1. Ammonium sulfate could be recovered from roasting off-gas by spraying after defluorination. Moreover, polyaluminum sulfate as a water treatment agent could be prepared from the leaching solution with the removal of F. The leaching toxicity of the leaching residue was accorded with the national standard.