A Head Mounted Display system suffers largely from the time lag between human motion and the display output. The concept of Reflex HMD to compensate for the time lag is proposed and discussed. Based on this notion, a prototype Reflex HMD is constructed. The rotation movement of the user's head is measured by a gyroscope, modulating the driving signal for the LCD panel, and shifts the viewport within the image suppliedfromthecomputer.Thederivativedistortionisinvestiated and the dynamic deformation of the watched world was picked up as the essenial demerit. The cylinderical rendering is introduced to solve this problem and is proved to cancel this dynamic deformation and also decrease the static distortion.