Many patients are diagnosed with malignant tumor in their daily work and are proposed to undergo surgery. However, due to the patient’s weakness and general malnutrition, he could not be operated immediately. Doctors are prepared to perform systemic nutritional support therapy for him and then perform surgery after his body gets better. After hearing this, the patient’s family members were often very anxious and approached the doctor: “Is it true that nutritional support therapy will “nourish” cancer cells and accelerate tumor development?” The relationship between tumor and nutrition is a topic that has been debated in the medical field for many years, and is also a problem that many tumor patients and their family members feel very confused. So, after suffering from tumor, should doctors give nutritional support treatment to patients? Should the family members give the patient turtle soup or chicken soup every day? Will nutritional support therapy really “nourish” cancer cells and accelerate tumor development? In fact, nutrient metabolism in human body is an extremely complicated process. Even if no nutritional support therapy is given to tumor patients, tumors still consume skeletal muscle in the form of vigorous glycolysis and damage the immune function of the body. In other words, even if a tumor patient does not eat or drink all day, the tumor can still grow wildly. Animal experiments also confirm that nutritional support can promote tumor cell proliferation. Without nutritional support, there is no treatment. Usually, malignant tumor patients have severe malnutrition, in which most of them cannot receive surgery, radiotherapy, chemotherapy and other tumor treatments. Giving nutritional support to tumor patients can help them complete various tumor treatments, completely kill tumor cells, improve their quality of life and prolong their survival. The incidence of postoperative complications and mortality rate are increased in malnourished tumor patients. Therefore, if effective nutritional support can be given one to two weeks before surgery, it can improve the whole body nutritional status of patients, reduce the occurrence of complications and decrease the death rate of surgery without delaying the surgery. Continuing nutritional support after surgery can accelerate the patient’s recovery. After radiotherapy, although the evil energy in the body is driven away, the positive energy is also damaged, and the patient’s energy consumption increases, resulting in adverse reactions such as decreased immunity and loss of appetite, which often force the treatment to be interrupted. In addition, giving nutritional support therapy can promote tumor cells to proliferate rapidly from quiescent phase to dividing phase, and tumor cells in dividing phase have increased sensitivity to radiotherapy. Therefore, nutritional support therapy during radiotherapy can not only increase the tolerance of treatment but also improve the therapeutic effect, which can be regarded as two birds with one stone. The supplementation of antioxidant nutrients while adjusting the nutrient balance of chemotherapy or radiotherapy patients can reduce the side effects of chemotherapy or radiotherapy, such as leukopenia, hair loss, nausea and vomiting. Meanwhile, β-carotene and selenium have the effects of inhibiting the expression of oncogenes and improving human immune function. In conclusion, nutritional support plays an important role in the treatment of tumor patients. Therefore, family members should fully communicate with oncologists and receive various treatments such as regular surgery, radiotherapy and chemotherapy on the basis of proper nutritional support in order to reduce the disease, improve the quality of life and prolong the survival period.