The present invention relates to a building asphalt preparation method. According to the building asphalt preparation method, one or the mixture of more of residual oil obtained in a crude oil distillation process, blended asphalt obtained in a blending process and deoiled asphalt obtained in a solvent deasphalting process is adopted as a base raw material, the base raw material is subjected to a cracking condensation reaction at a reaction temperature of 380-480 DEG C under an operation pressure of 0-0.1 Mpa under a residence time of 10-120 min in an upflow type visbreaking reaction tower, the obtained visbreaking product enters a reduced pressure fractionation tower to obtain components such as gasoline, kerosene, diesel fuel and lubricating oil, and the obtained tower bottom heavy oil is the building asphalt. According to the present invention, the method has characteristics of low production cost, low corrosion on equipment, reduced equipment use requirement, wide raw material source and flexible processing technology, wherein 10#, 30# and 40# building asphalts meeting the new standard of GB/T 494-2010 building petroleum asphalt can be prepared by adjusting process parameters.