The invention provides a low-noise continuously adjustable DC power supply and a modulation method thereof, wherein the low-noise continuously adjustable DC power supply comprises a switching power supply, a rectification filter unit, a DC voltage output unit of the switching power supply, and a DC voltage regulation output unit of a linear power supply, wherein after input direct current is regulated by the DC voltage output unit of the switching power supply, a voltage value, which is the total value of a voltage provided by a setter and a regulated voltage of a linear power supply compensating pipe, is output, and then regulated by the DC voltage regulation output unit of the linear power supply, so as to ensure that a voltage value output finally is in accordance with a voltage value provided by the setter. According to the invention, the low-noise continuously adjustable DC power supply can perform the advantages of both the switching power supply and the linear power supply, so as to realize the high efficiency, low ripple wave and continuous adjustment of the low-noise continuously adjustable DC power supply.