The utility model belongs to picked-fruit freshness keeping technology and particularly relates to a banana freshness keeping bag, a freshness keeping packing box and a method of adjusting gas composition content inside the banana freshness keeping bag. The freshness keeping bag comprises a membrane bag (1) and a preformed hole (4). An upper layer label (3) is arranged on the preformed hole (4) and used for controlling of opening and closing of the preformed hole. By adoption of the freshness keeping bag, the gas composition content inside the banana freshness keeping bag can be adjusted. Compared with the prior art, the method can enable the freshness keeping period of yellow ripe bananas to be prolonged by 5-7 days.