Limited studies have examined the associations between diet quality and gestational weight gain (GWG) among Chinese pregnant women, adopting Chinese GWG guidelines. We prospectively investigate the associations of diet quality, using the Chinese Healthy Diet Index for Pregnancy (CHDI-P), which assessed diet quality from 'Diversity', 'Adequacy' and 'Limitation' dimensions with overall 100 points, with GWG among participants enroled in Southwest China. Food consumption was collected by 24 h dietary recalls for three consecutive days and CHDI-P scores were divided into tertiles. GWG was calculated according to the weight measured before delivery and classified into adequate weight gain (AWG), insufficient weight gain (IWG) and excessive weight gain(EWG) following Chinese GWG guidelines. Multinomial regression analyses and stratified analyses by pre-pregnancy body mass index were performed to estimate the association between CHDI-P and GWG. A total of 1416 participants were recruited in early pregnancy, and 971 and 997 participants were respectively followed up in middle and late pregnancy. The mean CHDI-P score was 56.44 ± 6.74, 57.07 ± 7.44 and 57.38 ± 7.94 points in early, middle and late pregnancy, respectively. Women in the lowest CHDI-P scores group had an increased risk of EWG in middle (OR = 1.53, 95% confidence interval [CI] = 1.08-2.17) and late pregnancy (OR = 1.71, 95% CI = 1.21-2.41) than women in the highest group, while overweight/obese women had a greater risk of EWG in late pregnancy (OR = 4.25, 95% CI = 1.30-13.90). No association was found between the CHDI-P scores and IWG. Poor diet quality in middle and late pregnancy was associated with a higher risk of EWG.