The invention discloses a method for helically milling a hole and a device thereof. The method comprises the following steps: a cutting tool automatically rotates around the center line of the cutting tool and rotates around the center of a machining hole; when the size of the hole which is to be machined changes, a distance that the center line of the cutting toll departures from the center line of a stander is adjusted and the hole is continuously to be machined; and the cutting tool is used for continuously milling the hole according to predetermined feed rate until that the hole is machined. By adopting the method and the device, the cutting tool with diameter from 6mm to 8mm is used for machining the holes with different specifications, therefore, tool changing time is reduced, finish machining is avoided, and efficiency is greatly improved. The device also can have holes with high quality on the new materials such as carbonized fiber, titanium alloy, etc. Simultaneously, the device is portable, under the condition with the same precision, greatly reduces dependence to machine tools with large scale and high precision, can combine with manipulators, and can complete the work for milling holes with high precision in the whole assembly of an airplane whole components assembly.