Taking diphenylamine(DPA) as the raw material, three different kinds of alkylated diphenylamine (ADPA) antioxidants were synthesized by the alkylation of the raw material with 1-hexene, 1-dodecene and styrene in the presence of anhydrous aluminum chloride respectively. The structure of ADPA was characterized by IR and GC-MS, and the thermal stability and antioxidation performance of ADPA and L57 were investigated by TG and rotary bomb oxidation test respectively. In addition, the synergistic effect between ADPA and T501 as well as ADPA and ZDDP was also studied. The results showed that the content of disubstituted DPA at the para position is more than 80%. ADPA could increase the induce time of base oils 59 times at most when the additive amount is 1%. The synergistic effect between ADPA and the traditional antioxidant was influenced by molecular structure of ADPA.