The work aims to improve film-forming property of octadecylamine at low temperature. With pyridine and diisopropylamine mixture as solvent, auxiliary inhibitors were added into the octadecylamine solution for complex formulation. Uniform experimental was designed by taking pH, temperature and concentrations of each medicament as variable. Coupon test was performed by simulating water-vapor environment of power plant with an autoclave. Film-forming effect of the coupons was evaluated by performing CuSO4 dripping test and AC impedance test. Optimal compounding formula was obtained based upon chemometric calculation with polarization impedance as quantitative evaluation index. Optimal formula was as follows: 50 mg/L octadecylamine, 45 mg/L auxiliary A, 30 mg/L auxiliary B, 25 mg/L auxiliary C and 30 mg/L auxiliary D, pH=9.4 and film-forming temperature 100~130 ℃. Initial reddening time of the compound inhibitor film-formed coupons in CuSO4 dripping test was 41 s, and resistance of the protective film was 82 420 Ω?cm2. Compound can effectively improve film-forming effects of octadecylamine at nearly 100 ℃, and the formula can provide effective film-forming protection for low temperature equipment during standby period of power unit.