The invention discloses a low-carbon power supply investment decision-making method of a power capacity market under a new energy access condition. The low-carbon power supply investment decision-making method comprises the following steps of 1) building a mathematical model of the capacity market by taking low-carbon power supply installed capacity subsidy as an incentive method of the capacity market; 2) building a mathematical model of an electric energy market; 3) building a mathematical model of simulating a balance market; 4) building a comprehensive profit model of a power generation set according to the mathematical model of the capacity market, the mathematical model of the electric energy market and the mathematical model of the balance market; and 5) calculating annual comprehensive profit of the power generation set according to the comprehensive profit model of the power generation set, building a low-carbon power supply investment model of the power generation set according to the annual comprehensive profit of the power generation set, and estimating an investment state of the power generation set according to the low-carbon power supply investment model of the power generation set. By the method, the simulation of the capacity market is introduced to make a decision of low-carbon power supply investment of the power capacity market.