A device for oiling a moving yarn includes a controller, a housing, an oil port provided in the housing, and a dosing pump arranged in the housing. A yarn guiding device with an oil transfer element is mounted in the housing. The oil transfer element is connected to the oil port by an oil feed channel via the dosing pump. A closure element and a flow sensor are provided in the oil feed channel. The oil feed channel has a first portion from the oil port to the dosing pump, a second portion from the dosing pump to the closure element, and a third portion from the closure element to the oil transfer element. The flow sensor is provided in the second portion of the oil feed channel.

A method for preparing profiled fibers with low lousiness rate by a polyester FDY process is provided, when preparing profiled fibers by the FDY process, during the operation of a yarn path, the horizontal and longitudinal positions of wire guide ceramic pieces on the pre-entangling wire guide frame are adjusted to maintain vertical alignment of the filament bundle in the pre-entangling device and achieve optimal jitter effect, to prepare profiled fibers with a low lousiness rate; when the profiled fibers are triangular profiled fibers, the lousiness rate is 0.35-0.65%; when the profiled fibers are trilobal profiled fibers, the lousiness rate is 0.85-1.25%; when the profiled fibers are flat profiled fibers, the lousiness rate is 0.5-0.85%.