In the context of global energy transformation and the deepening reform of electricity market liberalization

combined heat and power (CHP) units must seek to maximize profits within a highly uncertain market environment. This paper proposes a day-ahead spot market bidding strategy for CHP units

grounded in information gap decision theory (IGDT). The strategy utilizes the IGDT model to quantify market uncertainty and integrates risk assessment with the Sharpe ratio (SR) to optimize the trade-off between profit and risk. Compared to traditional marginal cost methods and robust optimization approaches

comparative analysis reveals that the proposed strategy significantly enhances unit competitiveness and resilience against market fluctuations. Additionally

the paper explores the impact of varying heat loads on the bidding strategy of CHP units

providing both theoretical foundations and practical guidance for formulating more robust bidding strategies in the complex and dynamic power market environment.