In order to achieve ever more stringent demands on the CO2 emission reduction, 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 employed in a 1.8L turbo charged gasoline engine. By comparing the characteristics of ion-current signal under the engine operating conditions without knock, with knock and with different knock intensities, the wave signal of ion current differed apparently. The frequency spectrum of ion-current was also studied, by the method of discrete Fourier transform (DFT). In knocking cycles, there were fluctuations in 8-13 kHz frequency both in the combustion pressure signal and the ion current signal, proving knock information contained in them. 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.