Jumbo squid (Dosidicus gigas) dried squid thread were packaged in air, vacuum, modified atmosphere (40%CO₂₊₆₀%N₂), and modified atmosphere (40%CO₂₊₆₀%N₂) after treating with 0.5% citric acid, respectively. The changes in contents of formaldehyde, dimethylamine, trimethylamine, trimethylamine oxide, color difference values, thiobarbituric acid (TBA), total number of colonies, reducing sugar, amino acids and total protein were measured during room temperature storage, to investigate the effects of different packaging on changes of formaldehyde and quality indices of dried squid thread. The results showed that the contents of formaldehyde, dimethylamine, trimethylamine, and the value of a*, b*, TBA, total number of colonies increased during storage, while L* value and the contents of trimethylamine oxide, reducing sugar, amino acids (except for histidine), and myosin heavy chain (MHC), gradually decrease. The results indicated that trimethylamine oxide decomposed into formaldehyde, dimethylamine, and trimethylamine during storage. Meanwhile the browning occurred due to the Maillard reaction of reducing sugar and amino acids. Compared with air and vacuum packaging, modified atmosphere packaging could significantly inhibit the increase of formaldehyde and the bacteria growth, lipid oxidation and browning reaction in dried squid thread, and the modified atmosphere packaging after treating with 0.5% citric acid had the better effects.