In order to meet the ever more stringent demands on the CO2 emission reduction, downsized modern gasoline engine with highly boosted turbo charger meets new challenges such as super knock and pre-ignition, which will influence the engine combustion efficiency, smooth operation and even cause mechanical failure.A spark plug type ion current detection sensor was used in a 1.8L turbo charged gasoline engine. The ion-current wave signal differed greatly under different engine operating conditions such as without knock, with knock of different knock intensities. The frequency spectrum of ion-current was also studied, by the method of discrete Fourier transform (DFT). In knocking cycles, there were fluctuations of frequency 8-13 kHz both in the combustion pressure signal and in the ion current signal, proving the existence of knock information. After calculating the band filter signal and integral signal of ion current signal, both of them showed high linear relationship with knock integral signal. In pre-ignition cycles, ion current signals showed abnormal rise in amplitude before spark ignition signal and detected the pre-ignition events as precisely as cylinder pressure signal. Results proved that ion current detection was an effective method to evaluate knock intensity and pre-ignition fast detection in the downsized turbo charged engines.