The experiment aimed to explore the effects of different water contents and storage time on the content of mycotoxins in the mushroom bran of Flammulina velutifolia. This study set up 13%, 30%, 48%, 62%, and 76% moisture gradients of Flammulina velutifolia bran, and measured the content of aflatoxin B1 (AFB1), zearalenone (ZEN), ochratoxin A (OTA), and T-2 toxin (T-2) in Flammulina velutifolia bran, respectively. The dynamic changes in the content of Flammulina velutifolia bran naturally stored for 1~7 days were recorded, and the correlation between the content of each Flammulina velutifolia toxin and storage time was analyzed. Combined with the requirements of the Feed Hygiene Standard for the content of Flammulina velutifolia bran in feed raw materials, it was determined whether the Flammulina velutifolia bran exceeded the limit of mycotoxins. The results showed that at a moisture content of 13%, the contents of AFB1, ZEN, OTA, and T-2 in the mushroom bran of Flammulina velutifolia showed no significant differences within 1~7 days after storage (P>0.05), and none of them exceeded the standard threshold. At 30%, 48%, 62%, and 76% moisture content, the content of AFB1, ZEN, OTA, and T-2 in Flammulina velutifolia bran showed an increasing trend with prolonged storage time. At a moisture content of 30%, the content of AFB1, ZEN, OTA, and T-2 in the Flammulina velutifolia bran did not exceed the standard threshold. At 48%, 62%, and 76% moisture content, the content of AFB1, ZEN, OTA, and T-2 in the Flammulina velutifolia bran did not exceed the standard within 1~2 days after storage. At a moisture content of 62%, the content of AFB1 in the Flammulina velutifolia bran exceeded the standard threshold after the 3rd day, and all three contents exceeded the standard threshold on the 5th day. At 62% and 76% moisture content, both ZEN and OTA in the Flammulina velutifolia bran exceeded the standard threshold on the 7th, with T-2 content not exceeding the standard threshold. At low moisture content (13%), there was no significant correlation between fungal toxin content and storage time (P>0.05). Under medium to high moisture content (48% and 76%), there was a significant positive correlation between fungal toxin content and storage time (P<0.05), and there was a significant positive correlation between different fungal toxins (P<0.05). The study indicates that when safely storing Flammulina velutifolia bran, it is necessary to control the moisture content and storage time. When the moisture content of Flammulina velutifolia bran is below 13% or high moisture Flammulina velutifolia bran is used within two days of leaving the factory, it can ensure that the content of mycotoxins does not exceed the standard. [ABSTRACT FROM AUTHOR]