The invention provides a natural circulation coupling-type CFB steam injection boiler at the tail end of a direct current vertical evaporating pipe inside a boiler, and belongs to the technical field of oil field steam injection boilers. The problem of the pipe explosion caused by the heat transferring deterioration due to the fact that salt deposits are deposited on the inner wall of a water screen wall pipe of an existing natural circulation oil field steam injection boiler in the long-term is solved. A coal economizer is communicated with a two-side wall connecting pipe and a front-and-rear wall connecting pipe through a main water discharging pipe of the coal economizer. The two-side wall connecting pipe is communicated with an upper two-side wall collecting box through a lower two-side wall water screen wall collecting box and a two-side wall membrane water screen wall. The front-and-rear wall connecting pipe is communicated with a front-and-rear wall collecting box through a lower front-and-rear wall collecting box and a front-and-rear wall membrane water screen wall. The upper two-side wall collecting box and the front-and-rear wall collecting box are communicated with a steam pocket. Water space of the steam pocket is communicated with a water inlet of an evaporator through a descending pipe. A steam-water mixture outlet of the evaporator is communicated with a second steam-water separator through a third connecting pipe. A steam space of the steam pocket is communicated with a super heater through a steam connecting pipe. The natural circulation coupling-type CFB steam injection boiler is used for oil field steam injection.