Axial turbine is a key device which influences the power output and efficiency of the Compressed Air Energy Storage (CAES) system notably. In present study, the effect of chamber roughness on the efficiency and flow loss characteristics of an axial turbine in the CAES system is investigated numerically to find a way to improve the performance and reduce the manufacturing cost. The results illustrate that the efficiency is reduced nonlinearly with the increase of chamber roughness. An efficiency reduction of 0.45% is obtained when chamber roughness is less than 10 mu m at design point. However, the efficiency reduction of 1.9% is obtained by the chamber roughness of 50 mu m when the expansion ratio is less than 1.9. Internal flow analysis reveals that the passage vortex near upper end wall in the left-part of stator ring is strengthen with the increase of chamber roughness. An efficiency recovery of 0.61% is achieved by "Local smoothing wall" which has wall roughness of 1.6 mu m at only 11.26% of the wall area. The isentropic efficiency is also increased more than 0.6% compared to the full smooth wall wall when total pressure ratio is 1.4. (C) 2021 Elsevier Ltd. All rights reserved.