The present invention provides a reinforcing anti-crack agent for lime and fly ash materials, which comprises silicate mineral powder, gypsum or chemical engineering waste residue phosphogypsum and an alkali metal substance containing SO3, wherein the tricalcium silicate content of the silicate mineral powder is more than 55 percent; for the lime and fly ash materials or lime and fly ash aggregates, the early strength is quite low, the anti-crack performance is poorer; after doping the reinforcing anti-crack agent, the early strength of the lime and fly ash materials or the lime and fly ash aggregates is obviously improved, and other performances are also improved, and particularly the anti-crack performance is greatly improved, thereby effectively solving the problem that the road surface is easy to crack; and the industrial waste residue and acetylene residue are used to replace lime, and the poor-quality fly ash replaces the fly ash with second-level or higher level, thereby obviously lowering the construction cost and obtaining good economic benefits.