Objective To study and analyze the mycotoxins contamination status of Castanea mollissima in Huairou District during one year of cold storage. Methods Taking Castanea mollissima produced in Huairou District as the research object. Castanea mollissima samples of 5 varieties, including 3113, Huaijiu, Huaihuang, Yanhong, and Huahua were collected from the 4 highest yielding townships in Huairou District. They were stored in a cold storage for one year and sampled once a month. The content of 21 kinds of fungal toxins was determined by ultra performance liquid chromatography-mass spectrometry. Results During the storage period, a total of 11 fungal toxins were detected, including tentoxin, alternariol, tenuazonic acid, nivalenol, zearalenone, fumonisin B₁, fumonisin B₂, fumonisin B₃, alternariolmethylether, ochratoxin A, and sterigmatocystin. The detection rate and value of Alternaria toxins were relatively high. According to the analysis of sampling locations, the number of fungal toxins detected in the 4 townships increased from 66 to 79, with no significant difference or clear pattern. Based on the analysis of storage time, the number of fungal toxins detected in chestnuts showed an overall upward trend with the extension of storage time. The detection rate of fungal toxins was relatively low in the 1 to 6 months of storage, with 4-5 cases detected each month. By the 7th month, the detection of fungal toxins increased to 12 cases, and from the 9th month onwards, all 17 samples were detected. Conclusion The Castanea mollissima shall be consumed and processed less than 6 months of storage after harvest according to the perspective of mycotoxins contamination. The overall detection rate of fungal toxins shows a monthly upward trend. There is no regularity in the detection of fungal toxins in different chestnut planting areas and varieties, and there is co-contamination in Castanea mollissima samples during storage. Further analysis and research on the pollution risk of Alternaria toxins in chestnuts is needed.