The homemade lauric acid imidazoline quaternary ammonium salt corrosion inhibitor was compounded with organophosphonic acid as compound agent, and the synergistic corrodion inhibition effect of complex inhibitor in CO₂ saturated oilfield water was studied by using static weight-loss test method. The research shows that when the quaternary ammonium salt concentration is 60 ~ 80 mg / L, corrosion time is 32 ~ 48 h, and temperature is 50 ℃, the synergistic corrodion inhibition effect of lauric acid imidazoline quaternary ammonium salt and polyamine polymerorganophosphonic acid (PAMMP) is the best, and the synergism of quaternary ammonium salt with ethylenediamine tetramethylene phosphonic acid ( EDTMP) had a stable corrosion inhibition efficiency.