The intermediate heat exchanger (IHX) is one of the most important equipments of accelerator driven sub-critical power system (ADS) in which the heat transfers from high-temperature lead bismuth eutectic (LBE) to the low-temperature helium gas. The efficiency improvement and optimization of heat exchanger could improve the work capability of the power system. In present work, the LBE-helium two-loop cooling system based on ADS and a specialized experimental platform of IHX are introduced. The effects of inlet conditions on the exergy efficiency of an LBE-helium heat exchanger are investigated at the LBE temperature of 300-490 degrees C and the LBE flowrate of 1-200 kg/s. The unavoidable exergy loss of IHX is investigated using the method of advanced exergy analysis. The results indicate that the minimum of exergy efficiency of LBE-helium heat exchanger is presented when the LBE mass flowrate increases gradually. The decreasing inlet flowrate of helium gas is helpful to improve the exergy efficiency. When exergy losses of LBE and helium gas are the minimum value, the minimum value of exergy loss of IHX is obtained, and that is the unavoidable exergy loss. At conditions,of the fixed total heat transfer and area of heat transfer, the optimal ratio of unavoidable exergy loss caused by temperature difference and caused by pressure drop is obtained for the minimum exergy loss. These are practically helpful to improve thermodynamic process of IHX focused on the reducing avoidable exergy loss. (C) 2016 Elsevier Ltd. All rights reserved.