To accurately understand the formaldehyde in foods and provide scientific basis for food safety supervision, some problems on its origin and determination were discussed. Trace formaldehyde exists as a natural ingredient of many foods. Besides factitious addition, the formaldehyde in food may originate from physical and chemical reaction of some other ingredients of the food, and may be associated with the water and wrapping material used in the process of food production and method of determination. So evaluating the safety of foods containing formaldehyde must be scientific and careful.