Objective: To improve the storage safety of Xinjiang fresh walnut. Methods: Xinjiang "Xin 2" thin-skinned walnut was used as material, sterile water was inoculated as a control group, and Aspergillus flavus was inoculated as an experimental group. The Aspergillus flavus isolated and purified from naturally moldy walnut was artificially inoculated into Xinjiang thin-skinned fresh walnut with different water content （10%, 15%, 20%, 25%, 30%） to investigate the growth and toxicity of Aspergillus flavus. Results: The water content of walnut which was suitable for the growth of Aspergillus flavus and the secretion of Aflatoxin M₁ was 15%. With the increase of walnut water content, the growth of Aspergillus flavus increased first and then decreased, but the growth of each water content was different, and the growth of Aspergillus flavus was proportional to the content of Aflatoxin M₁. Conclusion: The water content of raw materials is closely related to the growth of Aspergillus flavus and the content of Aflatoxin M₁ produced.