AimsTo describe the changes in moderate‐to‐late preterm infants' (MLPIs) growth during 12 months of corrected age (CA) and to examine the predictive role of NICU‐related stress, postpartum depression trajectory and family coping ability on the physical developmental trajectory of MLPIs.DesignA prospective longitudinal study.MethodsThere were 237 mother–infant dyads with at least two follow‐up data records included. General characteristics and NICU‐related stress were recorded from medical records at baseline. Infants' physical growth was measured at 40 weeks, 1, 3, 6, 9 and 12 months CA during outpatient follow‐up. Maternal postpartum depressive symptoms and family coping ability were assessed by questionnaires at 1, 3, 6, 9 and 12 months CA and 1 month CA respectively. We investigated the modifiable factors inside and outside of NICU on the trajectories of physical growth in the first year in MLPIs, mainly by using latent growth curve models with time‐varying covariates.ResultsThe curved trajectories of weight, length and head circumference in the first year in MLPIs demonstrated gradually slowed growth rates and these infants were above the WHO growth standards for the same age and sex. The latent growth curve models indicated that more NICU‐related stress was negatively associated with the weight and length at 40 weeks CA, and family coping ability (parent–child relationship) at 1 month CA was associated with the growth rate of weight. Besides, more NICU‐related stress predicted faster length growth rate. The infants of mothers who were in the group of high‐level postpartum depression trajectory had a slower growth rate of head circumference.ConclusionsOur study identified the modifiable factors along the care continuum influencing the trajectory of MLPIs' physical growth. Nurses should receive more training about infant stress measurement and family‐centred care to work in partnership with parents so that MLPIs can reach their full developmental potential. Also, multidisciplinary interventions including stress reduction strategies, close psychological monitoring and education improving parent–infant relationships should be further developed to achieve optimizing growth in the first year of MLPIs.Implications for the Profession and/or Patient CareIt is recommended that nurses pay attention to the long‐term physical growth status of MLPIs, and closely support their families. Quantifying NICU‐related stress and developing reduction strategies should be the priority for clinical staff during hospitalization. After discharge, persistent screening of depressive symptoms, psychological intervention and education about the parent–child relationship need to be included in the follow‐up visits.Patient or Public ContributionNo patient or public contribution. The study only included patients who were research participants.