For interprovincial power sources, the determination of long-term agreement curves primarily relies on historical data from both power generation and consumption parties. However, DGWB systems equipped with thermal power plants and multi-timescale energy storage systems, which feature multi-energy complementarity, relatively controllable output, and a lack of historical data, often render traditional methods inadequate. To address these issues, this paper proposes a two-layer optimization model. Under nonlinear safety constraints such as peak demand during the evening peak period, DC curve platform, and curve achievement confidence level, the model aims to fully meet the power and electricity demand of the receiving area while maximizing the profits of the generating area, thereby achieving the optimization of DGWB's long-term agreement curves. Research indicates that this optimization model can enhance the economic benefits by increasing the proportion of renewable energy in the transmission channel (14.85%), reducing power purchase costs in the receiving area (2.45%), and improving profits in the generating area (3.79%). Additionally, it enhances safety by increasing evening peak supply capacity (11.5%) and reducing the difficulty of ramping during midday and evening peaks (7.9% and 10.7%), thereby achieving a win-win outcome for both the generating and receiving areas.