The invention provides a fault diagnosis method and device for a generator set air-inlet pipeline. The method comprises the steps of obtaining the inlet air pressure of the generator set air-inlet pipeline; detecting whether the drop rate of the inlet air pressure of the generator set air-inlet pipeline is higher than a set value or not; when the drop rate of the inlet air pressure is higher thanthe set value, judging whether the set revolving speed of a engine is lowered or not; when the set revolving speed is not lowered, judging whether the revolving speed of the engine is lowered or not;when the revolving speed of the engine is lowered, generating and outputting warning information used for representing an air-inlet pipeline fault. Quick location of the engine fault is achieved.