With the increasing demands of complex application scenarios, off-grid integrated energy systems have emerged as a highly promising solution, particularly suitable for remote areas without grid coverage. To meet system load requirements, efficient strategies such as system modeling and design optimization are of great significance, requiring a comprehensive balance between economic and environmental factors. However, the volatility, variability, and uncertainty of renewable energy generation and power supply pose significant challenges to the supply-demand balance of off-grid systems. To address this, this paper proposes a stochastic optimization method aimed at achieving the optimal design of off-grid integrated energy systems. The method incorporates the uncertainties of wind speed and solar irradiance to construct a bi-objective optimization model, which balances the reduction of pollutant emissions and the enhancement of economic benefits while adhering to equipment constraints and ensuring power balance. Additionally, this study introduces an innovative method for evaluating renewable energy penetration rates. Simulation analysis of a real-world project demonstrates the feasibility and effectiveness of the proposed model.