Based on the method of Gas Chromatography-Combustion-Isotope Ratio mass Sprectrometry (GC/C/IRMS), the contents of formaldehyde and the δ ¹³C value in aquatic products, dried edible fungi, fruits and vegetables were tested and analyzed. The results showed that the mass fraction of formaldehyde in the squid samples was 0.341~24.185 mg/kg, and the δ ¹³C value was -48.167‰~-24.514‰; the mass fraction of dragon fish samples was 54.555~121.416 mg/kg, and the δ ¹³C value was -45.430‰~-27.468‰. In the dried edible fungi, formaldehyde was detected only in dried Lentinus edodes of 212.741 mg/kg, and the δ ¹³C value were ranging from -41.293‰ to -20.293‰. Formaldehyde mass fractions were low in fruits and vegetables. The δ ¹³C value of aquatic products was gradually negative with the increase of the preservation time, while that of Lentinus edodes was gradually positive, possibally caused by different formaldehyde conversion pathways in food. The results showed that the contribution rate calculated by isotope quantitative analysis model was 15% less than its theoretical value.