A backlight module actuation method aims to modulate a unsaturated luminance cycle in a dimming cycle for a backlight module in the condition of a saturated luminance. An oscillation amplitude time series of the duty cycle of a transformer at the rear end is set according to the dimming cycle to form a switch kinetic energy in the unsaturated luminance cycle. The switch kinetic energy can eliminate the parasite capacitance generated when the backlight module is in the condition of the saturated luminance.