With the aging global population, the decline in muscle mass and function among the elderly has emerged as a significant concern. This systemic progressive generalized loss of muscle function and mass is referred to as sarcopenia (SP). In recent years, a growing number of studies have investigated SP, revealing that many tumor diseases, especially in the digestive system, promote its occurrence due to the influence of the disease itself, diet, and other factors. Moreover, SP patients tend to have poorer postoperative recovery. At present, many diagnostic methods have been developed for SP, but no unified standard has been established. Furthermore, the cutoff values of many diagnostic methods for different populations are still in the exploratory stage, and additional clinical studies are required to explore these issues. This article comprehensively and systematically summarizes the diagnostic methods and criteria mentioned in previous research, focusing on the impact of SP on post-surgical patients with various malignant tumors.