The present invention relates to a kind of loudspeaker and its preparation method. It possesses three different structure types: the described upper magnetic yoke and lower magnetic yoke are respectively one circular or rectangular or regular polygon flat-plate or concave flat-plate; the described upper magnetic yoke and lower magnetic yoke are respectively two circular or rectangular or regulator polygon concave flat-plate. The periphery of the flat-plate is equipped with Nd-Fe-B permanent-magnet steel wafer, and the described permanent-magnet steel wafer is pushed into the described pole-face gap from outside, and at the same time a hollow frame inserted in the concave flat-plate is used as slideway and positioning face. Besides, it uses a fastening piece made of magnetic insulation material to form a combined magnetic circuit which does not use adhesive between pole-faces.