The work aims to investigate the effect of different initial O2 concentrations (5%,10%, 21%, 50%, 75%) on quality of agaricus bisporus. The agaricus bisporus was quickly fumigated with 5 μL/L of 1-MCP for 12 h after being harvested, and then stored in incubator at 3 °C after MAP with different initial oxygen concentrations. Its O2 and CO2 concentrations, weight loss, texture, sourness, sweetness, bitterness, saltiness and umamiduring storage were measured. The changes on its nucleotides, color and other quality indexes were measured. The respiration of mushrooms made the O2 and CO2 concentrations inside the package change drastically. O2 was rapidly consumed, and CO2 gradually increased; the firmness of mushrooms in the high-O2 treatment group remained above 14 N, which was 27.36% higher than that in the low-O2 treatment group; the contents of flavor nucleotides were all in the medium range. 50% high-O2 treatment group had the lowest loss rate of flavor nucleotides (10.32%), and that of the other four groups ranged from 18.44% to 26.47%. In addition, both high and low-O2 treatment groups could inhibit enzymatic browning to a certain extent. Compared with day 0, the brightness values were all lower than 6.78%. Low-O2 treatment group especially had a better effect on delaying browning. The browning index of the 5% treatment group was 28.82, which the lowest in later storage, and was 12.85% lower than that of the control group. The respiration intensity of agaricus bisporusis linearly related to the initial O2 concentration, and the quality is also closely related to the O2 concentration inside the MAP. High-O2 treatment is more conducive to maintain the firmness, the level of flavor nucleotide and umami taste. In summary, 50% treatment group has good effect. Both high-O2 treatment and low-O2 treatment groups can inhibit the enzymatic browning of polyphenol oxidase to keep the mushrooms with good brightness and delay the browning of mushroom in storage, and the effect of low-O2 treatment is better than high-O2 and control treatment.