BackgroundWith aging, body mass index (BMI) increases and muscle strength declines, resulting in dynapenic obesity. It remains unknown whether and how sleep duration contributes to the sequence of BMI and muscle strength change in the progression of dynapenic obesity.MethodsData were derived from the first two waves of China Health and Retirement Longitudinal Study. Sleep duration was self-reported. BMI was calculated and grip strength (GS) was measured to reflect muscle strength. The effect of baseline sleep duration on the sequential change of BMI and GS was assessed using two mediation models considering the nonlinear associations between them. The moderating effect of metabolic disorder was also tested.ResultsTotally 4986 participants aged ≥ 50 years (50.8% females) with complete information on variables were included. Baseline BMI fully mediated the nonlinear association between sleep duration and follow-up GS change, but baseline GS did not mediate between sleep duration and follow-up BMI change for older men and women. Short sleep duration positively affected BMI-induced GS change (β= 0.038; 95%CI, 0.015–0.074), while this favorable effect became nonsignificant for moderate sleep duration (β= 0.008; 95%CI, -0.003–0.024) and turned negative with prolonged sleep duration (β=  − 0.022; 95%CI, − 0.051 to − 0.003). This nonlinear mediation effect was more pronounced in older women who are relatively metabolically healthy at baseline.ConclusionFor older adults in China, the influence of sleep duration on BMI-induced GS change but not the GS-induced BMI change suggested the contribution of sleep duration to the sequential course in the progression of dynapenic obesity. Sleep duration deviated either above or below normal range may confer adverse impact on GS through BMI. Strategies addressing sleep and obesity jointly to improve muscle function and delay the progression of dynapenic obesity are required.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12877-023-03857-7.