The invention provides an LED drive power supply and a controller thereof. The controller comprises a ground terminal, a sampling terminal, and a power supply terminal. The ground terminal and an output ground of a power supply module have different potentials. A drain of a power switching transistor is coupled to a positive output terminal of the power supply module, a source of the power switching transistor and the sampling terminal are coupled to a first terminal of a sampling resistor, and a second terminal of the sampling resistor is coupled to the ground terminal. The controller further includes a logic control circuit determining whether a sampling voltage input by the sampling terminal is zero; a driver generating a first driving signal to the power switching transistor; and a bias circuit configured to receive a power supply voltage.