In a real-world electricity market dominated by large-capacity units and large users，the possibility of price multiplicity cannot be ignored，and its influence is significant.In view of the problem of multiple dual solutions（MDS），this paper analyzes the nature of this problem，and proposes an incentive-based pricing method for this situation.First，based on a rational extension of the classical spot pricing theory，the theoretical range of spot price in a two-sided bidding mode is analyzed，and the concept of pseudo marginal bid（PMB）is put forward.Then through discussions about the incentives of market participants，an additional equation for PMB is developed to achieve a unique solution for the Lagrange multipliers，thus determining the nodal price.The theoretical analysis and case study show that the nodal price obtained with the proposed method is rational and incentive compatible.