A voltage regulation unit with a Zener diode receives a driving voltage outputted from a charge pump and controls a level of the driving voltage to regulate the driving voltage. The voltage regulation unit includes a current mapping unit, a Zener diode and a biasing unit. The current mapping unit receives the driving voltage and generates first and second current signals at master and slave current ends according to the driving voltage, respectively. The diode receives the first current signal and controls the level of the driving voltage to be substantially equal to a predetermined voltage level. The biasing unit receives the second current signal, judges whether the level of the driving voltage reaches the predetermined voltage level according to the second current signal, and outputs a control signal, which is fed back to the charge pump to control the charge pump to generate the driving voltage.