The invention relates to the field of household garbage incineration, in particular to a method for related devices for controlling the hearth pressure of a mechanical fire grate type household garbage incinerator, and in particular to a furnace negative pressure stable control method. The two sides of a hearth of the incinerator are provided with pressure monitoring points for monitoring the pressure changes of the hearth in real time. An adjusting type baffle is arranged at an inlet of an induced draft fan. An incineration line induced draft fan frequency-change speed-adjusting device is adopted. A self-control system monitors the hearth pressure and the operation conditions of the baffle at the inlet of the induced draft fan and the frequency-change speed-adjusting device. Hearth pressure numerical values monitored in real time are transmitted to a control logic; according to the logic judgment, the opening degree of the baffle at the inlet of the induced draft fan is fed back, the induced draft fan frequency-change speed-adjusting device is set as a pressure coarse-adjusting object, and the baffle at the inlet of the induced draft fan is set as a pressure finely-adjusting object; and according to the real-time changes of the pressure, the control logic outputs an adjusting command to the baffle at the inlet and the induced draft fan frequency-change speed-adjusting device, so that the hearth pressure is stabilized within the set range, and pressure fluctuation within a large range is avoided.