The present invention provides a backlight dimming circuit, a dimming method of the same and a liquid crystal display thereof. The backlight dimming circuit comprises a power supply voltage terminal VCC, which is used to provide supply voltage; an operational amplifier Q, the noninverting input terminal of which connected with the power supply voltage terminal VCC, and the inverting input terminal of which connected with a load terminal; a precision resistor R, which is connected between the noninverting input terminal and the inverting input terminal of the operational amplifier Q, the voltage differential signal across the precision resistor R being converted and amplified to a DC voltage signal by the operational amplifier Q and outputting; and a comparator C, the noninverting input terminal of which receiving the DC voltage signal output from the operational amplifier Q, and the inverting input terminal of which receiving a sawtooth signal from a boost IC in a boost converter, which is used to compare the DC voltage signal with the sawtooth signal of the boost IC and then outputting a pulse width modulation dimming signal according the comparison results. The structure of the present invention is simple, and the costs are low. The backlight brightness is associated with the screen in real-time, which reduces the backlight power consumption and promotes the energy conservation of the products.