Sarcopenia is a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength, leading to numerous adverse clinical consequences. It is particularly prevalent among ICU patients, often resulting in various poor prognoses, which has gradually garnered the attention of ICU physicians. The assessment methods for sarcopenia include muscle strength measurement, physical performance evaluation, and the measurement of muscle quantity or quality. Given the limited feasibility of muscle strength measurement and physical performance in critically ill patients, the assessment of sarcopenia in critically ill patients primarily focuses on measuring muscle mass or quantity. Various methods can be employed, including dual-energy X-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA), computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography (US), sarcopenia index (SI), and other techniques. Each method has its own characteristics, advantages and disadvantages for critically ill patients. We aims to provide necessary references for the clinical evaluation and scientific research of sarcopenia in critically ill patients.