Weakly cemented conglomerate of Tertiary system is a kind of special geotechnical material between soil and rock. It has low diagenesis degree and poor self-stability, and its characteristics of particle gradation and cementation degree have significant impact on engineering characteristics of the rock. The relationship among fractal characteristics, cementation degree, and shear strength of conglomerate was analyzed by screening test, particle size fractal characteristics study, and large-scale direct shear test on undisturbed and remolded samples taken from the weakly cemented conglomerate of Tertiary system in the tunnel exit of Menghua Railway of Zhongtiao Mountain. Research results show that weakly cemented conglomerate generally had binary fractal features in the boundary of particle size 1.0 mm, and the fractal dimension of fine particles was mostly less than that of coarse particles, which indicates that there are relatively more fine particles in weakly cemented conglomerate of Tertiary system, and the conglomerate with 1D fractal has optimal gradation and maximum shear strength. According to the degree of cementation, weakly cemented conglomerate can be divided into weak cementation and extremely weak cementation. The cohesion of extremely weak cemented conglomerate was negligible and its strength characteristics were similar to those of non-cohesive soil. Under the condition of similar cementation degree, the relationship between fractal dimension and tangent of internal friction angle of the conglomerate could be described by negative exponent function. The shear strength and internal friction angle of extremely weakly cemented conglomerate were only 33.46%-40.85% and 58.64% compared with weakly cemented conglomerate without considering the difference in particle gradation, which shows that the cementation degree is an important factor affecting the shear strength of weakly cemented conglomerate of Tertiary system.