Electricity forward market contract trading constitutes a principal trading method in the electricity market. To address deviations from or non-compliance with contracts in China’s forward electricity market, an Energy Deviation Settlement (EDS) mechanism has been implemented. However, the current EDS mechanism is marred by unscientific penalties and imprecise deviation cost assessments. Consequently, this paper proposes a deviation responsibility assessment method based on time-sharing trading prices. Initially, the total annual contracted power is decomposed to derive the hourly deviation power for all 8760 h of the year. Subsequently, considering the power supply cost and load level, this paper proposes four pricing strategies for typical supply–demand scenarios and constructs a time-sharing trading pricing model based on cost pricing. Finally, this paper conducts a simulation using actual electricity data from China’s Province H. The results demonstrate that, compared to the traditional EDS mechanism, the proposed method can more accurately and reasonably measure the value of deviation responsibility. Concurrently, it can be better integrated with the future development of real-time spot market operations.