The invention discloses a preparation method for asphalt with spinnable isotropic carbon fibers. The method comprises the following steps that 1, ethylene pyrolysis tar is used as a raw material and is purified after sedimentation and filtration; 2, flash evaporation is conducted on purified tar at the temperature of 280 DEG G-320 DEG C and under normal pressure; 3, then decompression flash evaporation is conducted on the material after the flash evaporation under the normal pressure; 4, medium-temperature asphalt is produced with the material after the decompression flash evaporation and coumaroneor other raw materials and mixed and melted in proportion; 5, polycondensation reaction is conducted on the materials after the mixed melting. The preparation method for the asphalt with the spinnable isotropic carbon fibers has the advantages that the process is simple and easy to industrialize, and no catalyst is adopted; the raw materials are abundant and low in price and cost; no waste residue is produced, waste liquid is discharged, and the method is good in environmental protection; high-temperature asphalt and modified asphalt which have various functions can be prepared through the adjustment of process parameters and the proportion changes of the raw materials.