Abstract: Using composite rawinsonde and tropical grid data, angular momentum budgets are analysed for periods covering sudden intensity change at the stage of typhoon for tropical cyclones in the western North Pacific. Main conclusions; angular momentum transfer can be used to diagnose the intensity change for the periods; the transfer at 850-300 hPa of the typhoon is important for the change in intensity; sea surface frictional dissipation is too great to be compensated by the angular momentum transfer in the typhoon inflow layer; any sudden intensification of typhoon must be supplemented by large mid-layer transfer of angular momentum in combination with significant anticyclonic wind shear acceleration between the middle and outflow layers.