Purposes <p>To establish age- and sex-specific percentile reference values for muscle mass and strength in the general population of Chinese adults.</p> Methods <p>This study used data from the China National Health Survey, including 13,794 adults aged 20–80 years for reference value construction and 3,733 adults for external validation. Muscle mass was assessed by bioelectrical impedance analysis, and muscle strength by a Jamar dynamometer. Sex- and age-specific percentile curves were generated using Generalized Additive Models for Location, Scale, and Shape.</p> Results <p>In males, whole-body muscle mass index (WMI) increased in early adulthood, peaked in midlife, and declined markedly after 60 years, whereas in females WMI peaked later and declined more gradually. Upper-limb and trunk muscle mass indices showed relatively stable patterns during midlife, while lower-limb muscle mass declined steadily with age in both sexes. Appendicular skeletal muscle mass index remained stable in early adulthood and decreased after midlife. Handgrip strength peaked in midlife in both sexes, and weight-adjusted handgrip strength remained stable until approximately 40 years of age before gradually declining. External validation demonstrated good calibration and consistency of the reference percentiles.</p> Conclusions <p>This study provides age- and sex-specific reference values for muscle mass and strength in Chinese adults.</p>