The invention discloses a two-stage injection drainage device and method for a coal-bed gas well wellhead. The device comprises a formation water inlet pipe, a coal-bed gas inlet pipe, a throttle mixing channel and a mixture fluid draining pipe, the coal-bed gas inlet pipe is sleeved with the formation water inlet pipe in a ring mode, the formation water inlet pipe penetrates through the coal-bedgas inlet pipe and stretches into the throttle mixing channel, and the coal-bed gas inlet pipe, the throttle mixing channel and the mixture fluid draining pipe communicate with one another in sequence; and the formation water inlet pipe is used for communicating with a draining pipe of a coal-bed gas well so as to make the formation water import, the coal-bed gas inlet pipe is used for communicating with a gas mining pipe of the coal-bed gas well so as to make coal-bed gas import, and the throttle mixing channel is a two-stage throttle injection mixing channel. According to the two-stage injection drainage device, from the structure of the two-stage injection drainage device, external power fluid does not need to be provided, twice injection drainage is conducted by relying on the gas andwater generated by the self coal-bed gas well, more coal-bed gas can be exhausted, the gas exhausting capacity is improved, and the efficiency of the two-stage injection drainage device is basically the same as that of a single-stage injection drainage device.