China's energy resources reserves are concentrated on the central and western regions. Meanwhile, the major energy demand is distributed in the eastern region. Large scale of cross-regional electricity transmission is implemented to guarantee the power supply. The long distance electricity transmission (LDET) cost is an essential component of the final detail price. This paper proposes a new method to evaluate the real cost of LDET, which mainly focuses on the price mark-up between the electricity exporter and importer. A weighted least square regression model is applied to evaluate the influence of the factors that could impact the real operating cost of the LDET. Furthermore, we apply the LDET cost model to evaluate the synthesize cost of renewable energy, and find the current renewable policy of China is inefficient.