Gear coupling component parts by the same number of teeth of the internal gear ring and band teeth flange coupling halves. The outer teeth into straight teeth and toothed drum-shaped teeth two kinds of so-called drum-shaped teeth is the outer teeth made of spherical spherical center on the axis of the gear, backlash than normal gear big drum gear coupling allow larger angular displacement relative to the direct gear coupling can improve tooth contact conditions, to improve the ability to transmit torque and prolong life. Gear coupling at work, two-axis relative displacement inside and outside surface of the teeth periodically for relative axial sliding inevitably lead to tooth wear and power loss, gear coupling need good lubrication and sealing state work.