The work aims to acquire HAP corrosion and scale inhibitor exhibiting the best corrosion and scale inhibition effects by analyzing corrosion and scaling in Block JX of Yanchang Oilfield, developing and screening formulas of corrosion and scale inhibitor specifically. The corrosion and scale inhibition performance of corrosion and scale inhibitor was evaluated at 90 ℃ in EDTA titration method, weighing method corrosion coupon analytical technique. Through repeated comparative analysis, the formulas were screened and field tests were carried out. Compared with that without corrosion and scale inhibitor, corrosion rate of water separated from oil well-produced liquid decreased from 0.125~0.161 mm/a to 0.023~0.034 mm/a, the corrosion efficiency reached over 80%. The amount of mixed scale reduced from 130~290 mg/L to 7~15 mg/L, the scaling inhibiting efficiency reached over 91%. Formulas of corrosion and scale inhibitor are screened in EDTA titration method, weighing method and corrosion coupon analysis technique. The corrosion and scale inhibitor exhibits excellent comprehensive performance. The corrosion and scale inhibition effect is remarkable in field tests at high temperature.