It was necessary to sterilize the oil-field re-injection water for biocorrosion inhibition. Saprophytic bacteria, iron bacteria and sulfate reducing bacteria were the three main microorganisms resulting in the microbial contamination. To enhance the sterilization efficiency of oil-field re-injection water by pulsed electric field (PEF), the combined treatment of PEF and ultrasound was explored in the study. Meanwhile, the effects of PEF, ultrasound and the combination treatment on the three bacteria inactivation were investigated. The combination treatment had higher inactivation efficiency than independent PEF as well as ultrasound. Obvious synergistic effects were also observed on the inactivation of saprophytic bacteria and iron bacteria by the combined treatment.