Siemens VDO knock detection algorithm is widely used in knock diagnosis in gasoline engine. However, the evaluating accuracy of knock is partly affected by the thought that the knock window is determined on the falling edge of cylinder pressure when knock occurs earlier than the peak pressure. VDO knock diagnosis expansion algorithm based on MWD (moving window domain) was proposed and the identification parameter △E_max was introduced to characterize the maximal accumulative high-frequency energy difference between a knock window and a reference window. By moving the reference window and the knock window within the area K, the knock calculation starting point can be detected accurately and more knock energy can be contained in the knock window. The ratio of the integral energy in the knock window and the reference window at this condition was defined as the knock factor. The result shows that the knock calculation starting point of MWD algorithm is earlier than the one of VDO method. It can present more knock energy information and avoid the missed diagnosis of the knock occurring earlier than the peak pressure.