Hydraulic fracturing technology has been widely used for oil and gas extraction in conglomerate reservoirs. It is a challenging task to accurately evaluate the fracturing effect. This study analyzed the main controlling factors of fracture complexity in conglomerate and proposed a new method to evaluate the fracturing effect. We used the discrete element method of PFC2D to simulate the hydraulic fracturing of conglomerate and compared the simulation results with in-situ fracturing characteristics. On the basis, the variation coefficient (CV) was proposed to quantify the fracture complexity. This method was verified by fracture complexity index (FCI) and stimulated reservoir volume (SRV). Results reveal that the fracture propagation pattern changes as the cementation strength increases. Under low gravel content, soft gravel and strong cementation, a single straight hydraulic fracture penetrating gravel is formed. Under high gravel content, hard gravel and weak cementation, complex fracture, mainly around gravel, is formed; The fracture is affected by gravel and propagates in the form of small failures with multiple deflection, termination, penetration and bifurcation, resulting in the fluctuation of the fracturing construction curve. The variation coefficient in statistics is introduced to measure the fluctuation amplitude of fracturing curve to evaluate the complexity of hydraulic fracture. CV is positively correlated with FCI and SRV. The larger the CV value, the more complex the fracture and the more significant the fracturing effect. These results indicate that the variation coefficient may be a new parameter to evaluate the fracturing effect in conglomerate.