Abstract: The four-electrode method was used to measure the fraction change in resistance (ρ_FCR) during the crack propagation of the concrete beam subjected to bending. The effect of carbon black(CB), steel fiber (SF) and carbon fiber (CF) content and their combination on the crack self sensing gauge factor (K) of the concrete beam was compared and analyzed. Based on the fractal theory, the effect of different conductive materials on the noise level of the normalized fractional change in resistance - crack opening displacement curve (ρ’_FCR-w’_COD) was studied. The results show that the linear fitting analysis fit well with the fraction change in resistance-crack opening displacement curve (ρ_FCR-w_COD) and K can be characterized as the slope of the fitted line. In addition, K decreases with the increasing of the SF content. The specimens with the addition of SF and nano CB reveal the best crack self sensing ability among all the specimens. K can be improved while the tortuosity of the ρ’_FCR-w’_COD curve is reduced by the addition of nano CB. Specifically, the K values exhibit an increasing tendency till the CB increases to a certain content and then K decreases for even higher content of CB. However, the fractal dimensions (D) of the specimens and CB content show an inverse tendency. Furthermore, the optimum dosage of nano CB is 1.0-1.5 kg/m³. There exists a negative effect on the K value with the addition of CF, however, the standard deviation of D of the ρ'_FCR-w'_COD curves is reduced for the specimens with CF.