Abstract: New energy with high permeability is profoundly changing the Day-ahead power balancing method, bringing problems such as power supply uncertainty at peak load, difficulties in overall management of power supply, and new energy consumption, due to which this paper proposes a Day-ahead power balancing method, in which new energy's predicted output is proportionally taken into account, considering both power supply protection and new energy consumption. Firstly, the relationship between the Taken-Into-Account Proportion of New Energy's Predicted Output (TIAPNEPO) in day-ahead power balancing reserve and power supply protection is analyzed, based on which a formula describing TIAPNEPO's upper limit is proposed, and key factors influencing the upper limit are also specially researched. Secondly, the relationship between TIAPNEPO and new energy consumption is analyzed, based on which a formula describing TIAPNEPO's lower limit is proposed. Lastly, based on TIAPNEPO's upper and lower limits, a comprehensive index is proposed to quantify the difficulty in the overall management of power supply protection and new energy consumption. All conclusions in this paper are verified using real power production data and true demonstrations.