A method for adjusting a common voltage of an LCD device includes providing an LCD device and a photodetector, obtaining variable parameters Ya, Yb and Yc, the variable parameters Ya, Yb and Yc respectively denoting flicker intensity of the LCD device when the common voltages are parameters Va, Vb and Vc, Vb exceed Va, and is less than Vc, when Yb exceeds Yc and is less than Ya, increasing the parameters Va, Vb and Vc respectively and repeating the two steps, when Yb exceeds Ya and is less than Yc, decreasing the parameters Va, Vb and Vc respectively and repeating the two steps, and when Yb is less than or equals Ya and is less than or equals Yc, setting an arbitrary value between Va and Vc as an optimum common voltage of the LCD device.