The utility model relates to an additive injection device, include: additive storage mechanism, additive injection pipeline, injector pump and first motor. Additive storage mechanism is provided withthe output tube that is used for exporting the additive. Be provided with first ooff valve on the output tube, output tube parallel connection injects the input of pipeline into to the additive. The injector pump sets up on additive ascending pipe way. The torque output axle of first motor links to each other with the torque input shaft of injector pump. When needs poured into one of them into andplant additive, the first ooff valve that will be used for saving on the additive storage mechanism's of required additive the output tube was opened to close other first ooff valves, first motor drives injector pump work, and required additive just injects the pipeline into through the additive and injects into to the soil body. Foretell additive injection device can online switch pours into into the additive, need not together to set up two above additive injection device, the installation cost is lower, and the operation is comparatively simple.