The utility model relates to a steam coupling system for a biomass incinerator and a coal-fired unit. A plurality of branch pipelines are additionally arranged on a steam outlet pipeline of an existing waste heat boiler, and steam is adjusted to enter different sections of a first-stage steam extraction pipeline and a high-pressure cylinder steam exhaust pipeline through different branch pipelinesaccording to the amount of steam generated by the waste heat boiler. When the amount of steam is small, the steam enters the first-stage steam extraction pipeline behind the steam extraction check valve to replace an original first high-pressure heater for steam extraction; when the steam amount is increased and the steam extracted by the first high-pressure heater cannot be completely consumed,redundant steam enters a first-stage steam extraction pipeline in front of a steam extraction check valve through a steam supplementing valve and returns to a coal-fired unit steam turbine high-pressure cylinder to do work for power generation; and when the steam amount is continuously increased, steam extraction by replacing a first high-pressure heater and acting by entering a high-pressure cylinder of a coal-fired unit steam turbine are combined, and steam cannot be completely consumed, redundant steam is coupled with exhaust steam in a high-pressure cylinder steam exhaust pipeline througha temperature and pressure reducer.