The invention discloses a regenerated modified slurry composition and a preparation method thereof. The regenerated modified slurry composition is prepared from the following components in parts by weight by wet grinding: 25-40 parts of regenerated micro powder, 10-15 parts of machine-made sandstone powder, 15-25 parts of straw ash, 3-5 parts of a reactive activator, 2-5 parts of a modifier, and 25-30 parts of mixing plant reclaimed water. According to the composition disclosed by the invention, the regenerated micro powder, the machine-made sandstone powder, the straw ash, the mixing plant reclaimed water and other wastes are comprehensively recycled, so that the waste utilization rate is high and conforms to green production and a concept of circular economy development.