The work aims to study effect of electrolyte composition on synergy of electrodeposition additives. An anionic surfactant-sodium octylphenol ethoxylate sulfate (OPES) was mixed with a cationic surfactant - dodecyldimethylbenzylammonium bromide (BDDAB) to make the mixed anionic-cationic surfactant as an additive. The effects of electrolyte composition on the synergy of additives were investigated in electrochemical method. Control performance of the mixed anionic-cationic additive on electrodeposition was understood by measuring carbon content and current efficiency. Inhibition efficiency of OPES-BDDAB mixed surfactant reached the maximum (71.5%) when the concentration of methanesulfonic acid in the electrolyte was 0.5 mol/L. The inhibitory efficiency increased with increase of Sn ion concentration, and the increase slowed down after the Sn ion concentration amounted to 0.1 mol/L. The proportion of anionic and cationic surfactants increased with the decrease of proportion of cationic concentration, and the inhibitory ability was poor. The carbon content of OPES-BDDAB mixture was the lowest (41.2 mg/L) and current efficiency (96%) was the maximum at the concentration of CMC (0.15 mmol/L). The electrolyte composition has effects on the synergy of anionic-cationic complex. Measurement results of carbon content and current efficiency show that both plating quality and control capacity over electroplating process can be improved by certain synergy produced by intermolecular interaction in the additives.