The invention relates to the field of carbon dioxide compressor performance tests, in particular to a carbon dioxide compressor performance test system with a transcritical/subcritical testing function. The system involves a test loop, wherein the test loop is formed on a main pipeline together with a to-be-tested carbon dioxide compressor; and the test loop comprises a first switching valve, a second switching valve, a third switching valve and a fourth switching valve which are arranged in sequence, wherein a transcritical circulating gas cooling section and a subcritical circulating condensation section which are connected in parallel are arranged between the first switching valve and the second switching valve, a transcritical circulating evaporation section and a subcritical circulating evaporation section which are connected in parallel are arranged between the third switching valve and the fourth switching valve, and the main pipeline is further provided with an adjusting and measuring assembly. The system has the advantages that the system covers the large-scale working conditions of the carbon dioxide compressor in transcritical/subcritical circulating, so that equipment used by test equipment is reduced, and the cost is reduced; and when different circulating tests are carried out through the same machine, disassembling and assembling of the machine are not needed, sothat operation is simpler and more convenient.