Abstract: The macro steel fiber and nano carbon black as conductive materials were added into the concrete to make smart concrete. A new type of concrete beam with double layers combined with the smart concrete and plain concrete was produced. In addition, the effect of the steel fiber content and the depth of the steel fiber-nano carbon black/concrete smart layer on the post-crack toughness and self-monitoring performance were studied in this paper. In order to monitor the concrete crack, four-probe method was used to measure the electrical resistance of the specimens. The results show that the toughness of the concrete beams is increased with the increasing of fiber content and the depth of the smart concrete layer. The crack self-monitoring of the concrete can be realized by analyzing the characteristics of the fraction change in resistance-time (ρ_FCR-t) curve. Furthermore, the ρ_FCR value is nearby zero before cracking, then a significant increase of ρ_FCR can be found after the crack appearing. If more than one crack happens on the smart concrete beam due to the deflection hardening behavior, new turning points where the slope of ρ_FCR-t curve changes can be observed. Additionally, the self sensing behavior decreases with the increasing of the steel fiber content and the depth of the smart concrete layer. The ρ_FCR value of the specimen increases rapidly after crack happening, after that it increases slowly gradually. However, the fractional change in resistance value at a certain crack width (ω_COD) decreases with the increasing of the fiber content and the height of the smart concrete layer. The proposed first order exponential decay function fits well with the ρ_FCR-ω_COD curves.