Objectives The relationship between sarcopenia and cognitive function has been extensively studied, but is usually explored at a single time point. We used repeatedly measured cognitive data to examine the relationship between sarcopenia and cognitive trajectories over time among middle-aged and older Chinese adults. Design A nationally representative cohort study. Setting and Participants Data were from three waves (2011, 2013 and 2015) of the China Health and Retirement Longitudinal Study (CHARLS). A total of 8963 participants with complete baseline data (wave 1) and at least two cognitive function tests (waves 1–3) were enrolled in this study. Measurements Sarcopenia was diagnosed at baseline (wave 1). The wave 1–3 data were used to analyze cognitive trajectories over time by constructing a latent class trajectory model (LCTM). Logistic regression model was used to analyze the association between sarcopenia and cognitive trajectories. Results Among 8693 participants, we identified two trajectories of cognitive function development, including a persistent low trajectory (n= 4856, 55.86%) and a persistent high trajectory (n= 3837, 44.14%). Sarcopenia was associated with persistently low cognitive trajectory of global cognitive (OR: 1.248, 95%CI: 1.046–1.490) after adjustment for other covariates. This association was still observed when stratified by age, gender, educational level, marital status, social activity, smoking status and drinking status. Mediation analysis showed that body mass index (BMI) mediated efficacy accounting for 42.32% of the relationship. Conclusions Our study showed two trajectory groups of global cognitive function. Sarcopenia was associated with a persistent low trajectory over time and BMI mediated the relationship between sarcopenia and cognitive trajectories among middle-aged and older Chinese adults.