Abstract: Objective To detect the diet behavior and influencing factors of related behavior at different stages among pregnant women. Methods Based on the Theory of Reasoned Action (TRA), literature review, expert evaluation and preliminary investigation, we designed and finalized three questionnaires. Diet behaviors among women in early term, medium term and late term were investigated by using the questionnaires. Results 624 early term, 619 medium term and 738 late term valid questionnaires were returned. Participants ranged from 18 to 45 years of age. 74% pregnancy body mass index (BMI) was within the normal range. More than 43% care taking was provided by the mother, followed by the husband. The participants had a good eating behavior on the whole. At 3 stages, carbohydrate intake, protein intake and fat intake were no significant difference when compared with that of recommended value (P>0.05). The pregnant women intaked insufficient cereal, beans, dairy and aquatic products, while fruit and nuts were more than needed (P＜0.05). Subjective norms influenced their eating behavior indirectly through influencing their behavior attitude and behavioral intention. The attitude could influence behavior directly without involving the intention. Conclusion The participants had relatively good diet behavior, but still had problems on food choice and a reasonable combination of a variety of food. Subjective norms influenced their behavior attitude and behavioral intention. The mother had the strongest influence on the pregnant woman’s diet attitude and behavioral intention among all those had direct contact with the pregnant woman.