Background <p>Age-standardised rates of motor neuron disease (MND) have declined in many settings, yet the absolute burden continues to rise in ageing populations. Whether this divergence is driven by demographic change or epidemiological shifts remains unclear, particularly in China.</p> Methods <p>Using data from the Global Burden of Disease Study 2021, we analysed trends in MND burden in China from 1990 to 2021. Decomposition analysis was applied to quantify the contributions of population ageing, population growth, and changes in age-specific rates. Age-specific incidence patterns were compared with global estimates, and key findings were validated against recent Chinese epidemiological studies.</p> Results <p>Despite declining age-standardised prevalence and DALY rates, the absolute number of cases and DALYs increased substantially. Population ageing accounted for 46.0% of the increase in DALYs, followed by population growth (35.0%) and changes in age-specific rates (19.0%). Age-specific incidence rates in China were consistently lower than global estimates. External validation demonstrated high consistency with national epidemiological studies.</p> Conclusions <p>The increasing burden of MND in China is primarily driven by demographic ageing rather than increasing disease risk. Declining age-standardised rates may mask growing healthcare demands in rapidly ageing populations.</p>