The invention discloses a steam turbine generator unit steam seal rub-impact on-line monitoring device. The steam turbine generator unit steam seal rub-impact on-line monitoring device comprises a sheet-shaped arc steam seal (2) with the H-shaped cross section, and the cross section of the steam seal (2) is matched with the cross section of an arc groove of an inner cavity of a steam turbine generator unit air cylinder (1) to be detected in size. The upper bottom face, facing the arc groove of the inner cavity of the air cylinder (1), of the steam seal (2) is provided with a plate spring (3). A strain gage (4) provided with a signal wire (5) is pasted to the plate spring (3). Compared with the prior art, the steam turbine generator unit steam seal rub-impact on-line monitoring device has the advantages that firstly, the rub-impact monitoring device can be installed at the important steam seal position according to actual requirements, and therefore the steam seal rub-impact fault of a steam turbine generator unit can be monitored conveniently in real time on line; secondly, early warning and later positioning can be achieved, the steam seal rub-impact slight and serious position can be accurately determined, and the fault processing blindness is avoided; thirdly, the device is simple in structure and easy to install and adjust.