The present invention discloses an LED backlight system and a display device. The LED backlight system includes an LED display module and an LED backlight control circuit. The LED display module includes LED string. The LED backlight control circuit includes a current module, a comparison unit, a control switch unit, and an impedance unit wherein, an input terminal of the comparison unit obtains a voltage at a negative terminal of the LED string, and when the voltage at the negative terminal is greater than a preset threshold voltage, the comparison unit controls the control switch unit to turn on such that the impedance unit connects in parallel with the current module so as to decrease the voltage at the negative terminal. Through above way, the present invention can prevent the unstability of the circuit loop in order to prevent the flicker phenomenon of the backlight system.