The invention provides a single-piece permeameter, a device for measuring a single-piece test sample and a measuring method. The single-piece permeameter comprises U-shaped double magnetic yokes, a frame, a primary winding, an H coil pair and a secondary winding, wherein the frame is positioned between the U-shaped double magnetic yokes; the primary winding is distributed on the frame; a to-be-tested test sample is arranged in the frame; the H coil pair is positioned below the to-be-tested test sample; the secondary winding is positioned in the primary winding; the secondary winding comprisesthree sub-windings which wind separately, namely a left-side winding, a middle winding and a right-side winging; each of the left-side winding, the middle winding and the right-side winding is provided with an input port and an output port; and one or more of the left-side winding, the middle winding and the right-side winding are selected to connect by connecting the input ports and the output ports of different sub-windings. Through implementation of the invention, the accuracy of measuring the intensity of the magnetic field of the to-be-tested test sample is improved; and magnetic propertyparameters in different areas of the to-be-tested test sample can be measured, the adaptability is improved, and the operation is simple and convenient.