The invention discloses a cutting device and method for building materials used in a construction site. The cutting device comprises a water collecting tank, a vertical plate I and a vertical plate II. The vertical plate II is arranged on the side, away from the vertical plate I, of the water collecting tank. The cutting device and method for the building materials used in the construction site has the beneficial effects that a pressuring machine, a water lance head, a water quantity valve and a water proof cover are arranged, so that the cutting edges of the building materials are more orderly, the cutting speed is accelerated, and the cutting efficiency is improved; a first filter plate and the water collecting plate are arranged, the dust produced by the building materials during cutting can be eliminated and collected, the health damage from the dust to workers is reduced, and the pollution of dust to the environment is reduced; a rolling device, a sliding device, a data interfaceand a controller are arranged, so that the pattern cutting process of the building materials is automatically completed, and the cutting efficiency is greatly improved; and a water pump, a water pumping opening, a water inlet pipe and a telescopic water pipe are arranged, so that the cutting tools of the building materials can be recycled without the need for consuming more resources.