New energy generation represented by wind power and photovoltaic is characterized by seasonal fluctuations and short-term stochastic volatility. With the large-scale grid connection of new energy sources, their output characteristics bring new challenges to the power balance of new power systems. In order to ensure the reliable operation of the power system, this paper investigates the multi-timescale-oriented power balance method. Firstly, the multi-timescale power output characteristics of new energy generation are analyzed in combination with the historical data of Fujian Power Grid from 2019–2022, the matching characteristics of new energy generation and load on different time-scales are summarized, and the current supply preservation problems and supply risks of Fujian Power Grid are analyzed in-depth; on this basis, the power system operation considering the medium- and long-term power balance and the short-term ionization balance is constructed On this basis, a simulation model of power system operation considering medium- and long-term power balance and short-term ionization balance is constructed. Finally, taking Fujian Power Grid as an example, by calculating the electricity power balance model under different time scales and analyzing the time-sequential production process with the participation of multiple forms of power generation, we quantitatively analyze the electricity supply shortage of Fujian Power Grid under large-scale new energy grid integration and put forward the relevant suggestions for balancing the adequacy of electricity power.