The invention relates to a method for preparing a plant extract for inhibiting orange post-harvest pathogenic bacteria, which comprises the following steps: drying the washed caulis impatientis at temperature of 45-50 DEG C, crushing and sieving the dried caulis impatientis with a 40-mesh sieve, and taking minus sieve powder for extraction; adding ethanol with the concentration of 70-95% based onfeed liquid volume ratio of 1:10 for carrying out ultrasonic circulated extraction at ultrasonic frequency of 30-40kHz at temperature of 45-55 DEG C for 3-5 hours; and carrying out reduced pressure concentration on the extract, and recovering a reagent so as to be prepared into a caulis impatientis stock solution with the content of 1g/mL. When in use, Tween 80 with the concentration of 0.01% is added to the stock solution of the extract to be diluted by 10 times. The orange fruits are soaked in the diluent for 1 minute, dried in the air, and packed into polyethylene film bags. The caulis impatientis extract has stronger inhibiting effect on the post-harvest pathogenic bacteria, belongs to a natural plant extract, and is used for retaining the freshness of the oranges without chemical residuals, health hazard to human bodies, and environmental contamination.