By investigating the relationship of pregestational body mass index(BMI), trimester-specific gestational weight gain (rate) during the first, second, third and total trimesters of pregnancy with adverse pregnant outcomes, to evaluate the effects of different pregestational BMI, trimester-specific gestational weight gain on pregnant outcomes, and to provide evidences for gestational weight control. From April 2015 to January 2016, 964 pregnant women in Zhejiang Taizhou First People's Hospital and Taizhou Huangyan Maternal & Child Care Service Center were enrolled in random for prospective study and were divided into groups according to the Institute of Medicine 2009 guidelines[IOM2009]. (1)They were divided into four groups according to pregestational BMI: low body mass, normal body mass, over body mass and obese group.(2)They were divided into three groups according to trimester-specific gestational weight gain (rate): normal gestational weight gain, insufficient gestational weight gain and excessive gestational weight gain.(3)The gestational weight gain and pregnant outcomes were recorded by using self-made information table, including the incidence rates of gestational diabetes mellitus (GDM), neonatal birth weight (BW), hypertensive disorders complicating pregnancy (HDCP), cesarean section, pliers delivery, shoulder dystocia, fetal macrosomia, small for gestational age (SGA), premature rupture of membranes, neonatal asphyxia, and neonatal hypoglycemia. (1)In this study, 964 pregnant women were enrolled, no significant differences were found in terms of age, culture level, pregnancy times and delivery times of the different pregestational BMI groups (>0.05). (2)The incidences of GDM, HDCP, premature rupture of membranes, cesarean section, pliers delivery, shoulder dystocia, fetal macrosomia, SGA, neonatal asphyxia and neonatal hypoglycemia were as dependent variables and trimester-specific gestational weight gain (rate) was as independent variable.Multivariate Logistic regression analysis showed that the pregnancy obesity was associated with increased risks of GDM and HDCP, the values were 6.63 and 2.60 (<0.05). The excessive gestational weight gain (rate) of the total trimester of pregnancy was associated with increased risks of GDM, fetal macrosomia and cesarean section, the values were 2.05, 1.36 and 1.60, (<0.05). There was no statistical significance in other groups (>0.05). (3)Compared to the normal groups, the pregnancy obesity and excessive gestational weight gain of the first, second, third and total trimesters of pregnancy were all associated with an increased risk of GDM, the values were 7.36, 1.61, 1.81, 2.20 and 2.4 (<0.05), respectively.The incidences of HDCP, cesarean section and neonatal hypoglycemia in pregnant women with GDM were higher than those in normal pregnant women (<0.05). There is a significant correlation among pregestational BMI, gestational weight gain (rate) during the first, second, third and total trimesters of pregnancy with adverse pregnant outcomes, and it suggested that we could reduce the incidence of adverse pregnant outcomes by pre-pregnancy BMI and gestational weight control, and the focus should be placed on pre-pregnancy BMI control.