The performance of a scroll expander modified from compressor was tested in an organic Rankine cycle (ORC) system. The ORC system mainly consisted of evaporator, scroll expander, plunger pump and condenser. The test rig employed R123 as working fluid. A natural gas furnace was employed as the heat source whose flue-gas temperature was about 250℃. The maximum output power of the expander was 1200W and the maximum isentropic efficiency of 48.2% was achieved under the testing conditions. In the second part, a 2-D model was established to simulate the working process of the scroll expander by the approach of computational fluid dynamics (CFD).The variation process of the pressure of the scroll expander was investigated with this method.