The invention discloses a picking head assembly of a fully automatic cotton picker, comprising a driving motor, a cylindrical picking head housing, a needle wheel barrel and a spring convey mechanism. A picking head in needle wheel barrel structure is adopted and passes through a gap in a free state of cotton plants horizontally to distribute the cotton flowers evenly within 360 degrees peripherally. During leafiness period, cotton leaves and flowers are not destroyed when cotton is picked. Therefore, the cotton can be picked for many times step by step and divided into classes; the picked cotton is separated directly from impurities, for instance, cotton leaves, cotton stems and the like, thereby the cotton picked during picking is prevented from being polluted, and the impurity ratio of the cotton is reduced; the cotton picking head automatically rotates within 360 degrees, thereby ensuring high-level cotton picking ratio and the final picking ratio of 98% above; and the spring convey mechanism separates and conveys the cotton from the needle wheel barrel by utilizing the spiral convey theory. Cotton fiber is not destroyed to ensure the quality of the cotton; the invention has no special requirements for subsequent processing device and reduces the subsequent machining cost.