Abstract: In order to evaluate the energy efficiency of long-distance steam pipe, the exergy efficiency is proposed as an important evaluating indicator to determine the energy efficiency of the steam pipe. A one- dimensional model for flow through steam pipe is established. And then the thermal efficiency and exergy efficiency of the 2 km-long steam pipe are calculated. The calculation results show that under constant steam flow rate , with the increase of the pipe diameter, the steam flow rate in the pipe as well as the pressure loss and thermal efficiency of the pipe will continuously decrease. However, the exergy efficiency of the pipe will increase at first and then decrease, with a maximum value in between. If exergy efficiency of steam pipelines is prioritized as the design target, compared with the existing design specifications, the steam pressure loss in the pipeline will be reduced as a result of the flow rate decrease. As long as enough steam pressure for the user is ensured, the extraction pressure of the steam turbine is allowed to be reduced substantially. At the extraction flow of 250 t/h, the turbine can output an additional 3330 kW of electrical power due to reduced extraction pressure. Therefore, it is more reasonable to select the steam flow rate in the pipeline within the range of 0~25m/s according to the investment cost.