NOVELTY - Preparing bio-oil from municipal sludge by supercritical pyrolysis process, comprises placing the factory sludge in a sealed high pressure reaction kettle, introducing inert gas, opening exhaust valve pressure to an atmospheric pressure state, then closing the valve, pressurizing the kettle with the inert gas, repeating the operation, pyrolyzing the kettle, performing catalytic process to supercritical water, standing the sludge supercritical water, cooling and collecting solid-liquid mixture, vacuum filtering the solid-liquid mixture, and then carrying out oil-water separation.    USE - The method is useful for preparing bio-oil from municipal sludge by supercritical pyrolysis process(claimed).    ADVANTAGE - The method prepares bio-oil with higher added value and without secondary pollution of heavy metal.    DETAILED DESCRIPTION - Preparing bio-oil from municipal sludge by supercritical pyrolysis process, comprises: (a) directly placing the factory sludge of the sewage treatment plant in a sealed high pressure reaction kettle, introducing inert gas, opening exhaust valve pressure to an atmospheric pressure state when the pressure in the kettle reach 0.1 MPa, then closing the valve, pressurizing the kettle with the inert gas, repeating the operation for 3-5 times to change the pyrolysis environment to an inert atmosphere; (b) pyrolyzing the kettle at 350-500 degrees C under a pressure of 22-25 MPa when the water content in the raw material sludge reaches supercritical state, performing catalytic process to supercritical water to realize sludge supercritical water under steam pressure, standing the sludge supercritical water for 1 hour to reach final pyrolysis temperature; (c) cooling and collecting solid-liquid mixture after the reaction, carrying out vacuum filtering to the solid-liquid mixture to obtain reaction product, and then carrying out oil-water separation. An INDEPENDENT CLAIM is included for bio-oil preparing device comprising a reaction kettle, a cooling pipe, a condenser, a filter, a vacuum pump and a liquid separator, where: a front end of the reaction kettle is equipped with a nitrogen storage tank, a booster pump and a high pressure gas storage tank; the upper part of the reaction kettle is connected with a top end of the pipeline, which is provided with a valve and a pressure gauge; the reaction kettle is provided with a sampling port; the sampling port is connected with the cooling pipe and the condenser whose two ends are respectively provided with a liquid collecting tank and a gas collecting bag; the reaction kettle is further provided with a rotating discharge hole; the rotating discharge hole is connected with the filter, the liquid distributor and a rotary evaporator; and the vacuum pump is connected with the liquid distributor, which is connected with the liquid collecting tank.