The Legal Aid Law of the China, which came into effect on January 1, 2022, has pushed the systematization of legal aid to a new height. However, against the background of the continuous improvement of the system, China's legal aid practice still faces many difficulties. The countermeasures to overcome these difficulties may not only need to improve the legal system, but also clarify the legal theory behind the system and the concept behind the practice. Therefore, in the context of the reform of the legal aid system, it is necessary to clarify the erroneous understanding of the concept of legal aid. This erroneous understanding mainly includes interpretations of willpower and utilitarianism. The willpower concept of legal aid mainly includes three forms: aristocratic spirit, religious enlightenment, and elite consciousness. They base legal aid on moral ideals, but there are drawbacks such as unstable supply and unequal personality. The utilitarian concept of legal aid mainly includes two forms: market behavior theory and government behavior theory. They base legal aid on practical interests, posing a threat to the inherent ethical values and independence of the legal profession. The concept of legal aid should be a contractual concept, which includes two levels of contracts, namely the original contract centered on the principle of fairness, as well as the "lawyer society" contract and the "lawyer state" contract as sub contracts. The concept of contractual interpretation absorbs the advantages of willpower and utilitarianism, and discards its shortcomings. It mainly has four advantages: firstly, it connects ethical and utility values, enabling the lawyer profession to achieve a balance between earning profits and maintaining legal aid enthusiasm; Secondly, the concept of responsibility has been restructured to shift from passive to active; Thirdly, the legal aid model has been updated, transforming it from a unidirectional state power to a multi-dimensional and diverse implementation; Fourthly, it reshaped the state of mutual respect and protected the self-esteem of the recipients. The spirit of China's lawyer system reform is consistent with the contractual concept, which can provide useful enlightenment for the construction of China's legal aid system: the basic right positioning of the lawyer's right to help, the multiple participation mode of legal aid, the detailed rules of legal aid practice, and the cultivation of legal aid awareness.