BackgroundMany primiparous women usually encounter various parenting and mental health issues after childbirth. The effects of intervention based on internet platform on parenting and mental health outcomes for Chinese first-time mothers remain unknown during the COVID-19 pandemic. Therefore, our research aimed to evaluate the effectiveness of an internet-based support program (ISP) on maternal self-efficacy (MSE), postpartum depression (PPD) and social support for primiparous women amid the pandemic.MethodsA multicenter randomized controlled trial (RCT) was conducted. From May 2020 to March 2021, 242 primiparous women were recruited in the maternity wards of two hospitals in Shenzhen City, China and randomly assigned to the intervention group and the control group. Women in control group (n = 118) received the routine postpartum care, and women in intervention group (n = 118) accessed to the ISP intervention (expert education and peer support) and routine postpartum care. Intervention outcomes were measured at baseline before randomization (T0), post-intervention (T1), and three-month follow up (T2) through questionnaires. The chi-square (χ2), the independent sample t-test and the repeated measures multivariate analysis of covariance were performed, and the two-tailed p-value