Low carbon energy transformation under the dualcarbon target will promote wind power, photovoltaic and other new energy gradually become the main power supply in China. But intermittent output of new energy needs enough system regulation ability to support its stable power supply, which brings great challenges to the flexibility of new power system. Based on the operation requirements of Beijing -Tianjin -Tangshan new power system,some flexibility improvement strategies are put forward, such as the flexibility transformation of thermal power units, the comprehensive demand response based on virtual power plants and the response mechanism based on flexible loads. Secondly, a full time series system operation model considering the flexibility resource constraints and multi-day coordinated operation is constructed. Finally, an empirical simulation is carried out through the Beijing -Tianjin-Tangshan planning system to realize the flexibility improvement scheme selection considering the operation economy, environmental protection and efficiency multi-dimensional benefits, which provides a reference for the future planning and construction of new power systems.