Boiler outfire events due to two completely different causes occurred on boiler No.1 of Dawukou Power Plant and boiler No.2 of Huaneng Beijing Power Plant have been analysed. On the basis of diagnotic tests

their solution methods are suggested as follows: (1) for outfire due to excessive oxygen

the secondary air velocity and oxygen quantity can be lowered

and the operation mode of shrunkenwaist air distribution being adopted; (2) for outfire due to serious lack of oxygen

the coefficient of excess air at outlet of the burner

the ratio of primary air and fuel

as well as the air temperature at outlet of coal pulverizer can be enhanced. After adopting abovementioned measures

similar outfire events haven't again occurred on the two said boilers.