A real-time dispatching decision evaluation method based on the idea of perfect dispatch assessment implemented by PJM power market is proposed to analyze and evaluate the real-time dispatching job accurately. The idea of perfect dispatch assessment implemented by PJM power market is firstly analyzed. Based on the real-time dispatch actual business, this paper proposes a real-time dispatching decision evaluation model including scene re-construction and evaluation indexes calculation by introducing the idea of perfect dispatch assessment into the real-time evaluation. The model could quantify the difference between real dispatching plan and the perfect one and make the real-time dispatching evaluation more objective. The test model based on the real power grid data from a province in China certifies the validity of this method.