Abstract: Replacing high-carbon fossil energy with zero-carbon and low-carbon renewable energy is the most important way to achieve carbon neutrality. Energy substitution needs legal system as the external guarantee，and marketization is the ultimate destination of renewable energy. And guaranteed acquisition and competition are typical measures of policy and marketization. Energy substitution path based on this background is facing difficulties such as alienation of system practice，vague administrative functions，unbalanced promotion mechanism，conflict between acquisition and competition rules，disorderly competition， etc.， which cannot meet the needs of high-quality development of renewable energy. In order to alleviate these difficulties and promote the high-quality development of renewable energy， it is necessary to further interpret the legitimacy of compulsory obligations. At the same time， the system design should， under the guidance of the principle of efficiency， clarify government functions， balance guarantee and competition， and effectively link up with the consumer-side consumption guarantee mechanism and the consumer-oriented incentive mechanism to jointly promote the substitution process of renewable energy.

Key words: guaranteed acquisition, competitive mechanism, energy substitution, renewable energy, carbon neutrality