Abstract: The correction of end profile plays a key role on the performance of the scroll machinery. The paper provides a method of double circular arc correction and its effect on the performance of the scroll compressor expander unit is investigated. A new assessment criterion of energy conversion efficiency is defined and different conditions including the supply pressure and the loads are considered in the experiment. Results show that the shaft power and the energy conversion efficiency can be improved effectively, which is caused by the increase of the suction chamber volume after the profile correction. It gives a basis for the further structure optimal design.