The fact that the paver can pave a flat road is caused by the floating principle of the paver screed. During the operation of the paver, the screed is in a floating state. Various forces on the screed, such as the weight of the screed itself, the buoyancy of the material, the traction force of the paver host and the resistance of the material are all in a state of balance, so that the height of the rear edge of the paver screed remains unchanged, thereby paving the Flat surface. If the external interference, such as the main body of the paver floating up and down caused by the original unevenness of the roadbed, will bring about changes in the elevation angle of the screed, thereby affecting the flatness of the layer. The function of the self-leveling device is to cause the elevation angle of the screed When the changing factors of , automatically pass the movement of the leveling cylinder, keep the position of the drag point A unchanged, eliminate the interference and pave the smooth road.