In recent years

renewable energy sources such as wind and solar power have rapidly increased their share in China's energy mix and are progressively replacing fossil fuels as the dominant power sources in the electricity system. Under this profound transition

the proportion of flexible regulation resources like traditional thermal power has significantly decreased. System operations have become more dependent on renewable resources

while uncertainties on both the generation and demand sides have surged. These multiple factors have made the risk of supply-demand imbalance increasingly prominent in renewable-dominated power systems. To address this risk

it is imperative for the system to fully exploit the regulation potential of both renewable energy sources and flexible loads. However

such regulation measures conversely affect the actual level of uncertainty faced by the system. The creates a bidirectional strong coupling relationship between system operations/planning decisions and uncertainty. This coupling fundamentally alters the mechanisms of system supply-demand balance

posing significant structural technical challenges to decisions. As the first paper in a series

this paper proposes the decision-dependent uncertainty (DDU) theory of renewable-dominated power systems. First

it provides a comprehensive analysis of the sources and categorization of DDU. Then

a unified model for supply-demand balance considering DDU is established

and the challenges posed by DDU to supply-demand balance are analyzed. Finally

the study summarizes the critical impacts of DDU on supply- demand balance in renewable-dominated power systems and offers theoretical support for supply-demand balance decision-making in areas such as operation and planning.