BACKGROUND: The relationship between childhood and adulthood socioeconomic status (SES) and long-term frailty trajectories is unclear. We aimed to assess the frailty index (FI) dynamic trajectories and examine the associations between childhood and adulthood SES and frailty trajectories. METHODS: We included 7321 participants aged 45 and older from the 2011-2020 China Health and Retirement Longitudinal Study (CHARLS). Six childhood SES factors and four adulthood SES factors were included. Group-based trajectory modelling was used to identify frailty trajectories and multinomial logistic regression was used to assess the association between SES and frailty trajectories. RESULTS: Three frailty trajectory groups were identified: low-increase trajectory (LT, 59.9 %), moderate-increase trajectory (MT, 31.7 %) and high-increase trajectory (HT, 8.4 %). With the LT group as reference, for childhood SES, participants with an illiterate mother (relative-risk radio [RRR]=1.67, 95 % confidence interval [CI]: 1.10-2.52), having not enough food (1.67, 1.34-2.09), with family's financial situation (2.35, 1.61-3.42) and childhood health status (2.72, 2.09-3.53) worse than others had higher odds of being in the HT group. For adulthood SES, rural residence (1.86, 1.50-2.31), with an educational level of less than middle school (2.75, 1.83-4.15), had higher odds of being in the HT group. Similar results were found for people of different ages, genders, and residences. CONCLUSIONS: Participants with lower SES, including maternal and self- low education, childhood hunger, worse family financial and childhood health status are more likely to experience a high-increase FI trajectory, i.e. aging faster. Attention should be paid to reduce early-life social inequalities thus to promote later-time healthy aging.