The purpose of this study was to optimize the extraction process of citronella essential oil using ultrasonic-assisted steam distillation and to evaluate its effect on keeping the freshness of gold pomfret. The optimization was carried out using single factor and orthogonal array design experiments. The effect of citronella essential oil emulsion on keeping the freshness of gold pomfret was evaluated by measuring its thiobarbituric acid reactive substances (TBARS) value, total volatile basic nitrogen (TVB-N) content and freshness quality index (K value). The optimal extraction conditions were as follows: solid-to-solvent ratio 1:25 (g/mL), ultrasonic time 30 min and ultrasonic power 260 W. Under these conditions, the average yield of citronella essential oil was 6.77%. Citronella essential oil emulsion reduced the TBARS value, TVB-N content and K value of gold pomfret during storage. Citronella essential oil can keep the freshness of gold pomfret.