he principle of crankcase ventilation system for a turbocharged gasoline engine was expounded. The blow-by flow, fresh air supplement, oil carry-over amount, and oil consumption tests were conducted. The bench measuring method of oil carry-over amount for oil-gas separator was generally introduced and the oil carry-over amount difference was measured under different blowby flows and numbers of oil-gas separator fine separation hole. It was found that during the process of experiment whether the reverse cut-off function of oil return check valve on the oil return channel of oil-gas separator was reliable or not would directly affect the test result. The test results show that the oil carry-over amount of the designed oil-gas separator can meet the design requirements under the condition of single or double blow-by flow. And the overall oil carry-over amount achieves a high level when the number of fine separation hole is 4.