Cachexia is one of the most common complications of cancer. The prominent clinical feature of cachexia is muscle wasting. And protein degradation in skeletal muscle is important in the pathophysiology of cachexia. Cachexia can caused by abnormal metabolism of skeletal muscle in cancer patients resulting from increased energy expenditure and invalid energy utilization. Also, the muscle microenvironment is closely associated with the development of cachexia, many biological factors could directly or indirectly lead to proteolysis and skeletal muscle atrophy. It is estimated that cachexia occurs in half of cancer patients, and is responsible for the death of 20%~40% of malignant cancer patients. Cachexia is distinct from starvation, stress-related loss of muscle mass and has severe consequences. Current interventions cannot reverse its process; therefore, it is important to measure body composition, observe the dynamic changes of skeletal muscle and implement nutritional intervention as early as possible.