Abstract: Yang being solid is an important summary of the normal functional state of yang qi in The Yellow Emperor's Inner Classic. Based on the theory of yang being solid and able to hold on, it is proposed that yang being solid is essential to maintain the state of tightness, thoroughness and quietness for maintaining the health of the human body. Yang losing its solidity is the core pathogenesis of the onset and progression of malignant tumors, which manifests as yang deficiency, yang depression and yang restlessness. If yang is not solid due to its deficiency, yang will lose its warmth and defense and the evil qi will be retained; if yang is not solid due to its depression, yang will lose its warmth and circulation and phlegm and stasis will gather; if yang is not solid due to its restlessness, yang will lose its tranquility, burn yin and consume essence. Aiming at the core pathogenesis of yang losing its solidity, the treatment methods of warming yang and replenishing qi to treat the disease before it occurs, unblocking yang and removing turbidity to disperse the staleness, and clearing and resolving restless yang to fight cancer and detoxify are used in clinical practice. Restoring the solidity of yang is taken as the goal of treating malignant tumors, which provides ideas for the clinical practice of treating malignant tumors with traditional Chinese medicine.