The arching phenomenon in the core of earth-rock dams plays a crucial role in ensuring their safety and stable operation. The mechanical properties of the core are influenced by various factors, including complex topographic and geological conditions. This study investigates and compares the arching behavior of vertical cores, inclined cores, and lower straight upper inclined cores. Additionally, slope gradient, valley width, and overburden thickness are selected as parameters to characterize the topographic and geological conditions of the dam. A quantitative analysis is conducted using numerical calculations to examine the influence of complex geological conditions on the arching behavior of asphalt concrete cores. The findings reveal that the stress arching in the core is predominantly concentrated near the middle 3/4 of the core height and along the bank slope. The arching effect in the inclined core is relatively small, contributing to an overall improvement in the core’s force distribution. As the bank slope steepens, the arching strength in the inclined core increases, resulting in a wider area of stress transmission extending from the middle of the core to both sides of the slope. Increasing the valley width causes the stress transfer concentration to gradually shift from the core’s bottom to its sides and upper part. The overall stress arching in the inclined core does not exhibit a monotonic relationship with the increase in valley width. When the ratio of dam axis length to dam height reaches 3 to 4, the valley effect significantly reduces deformation and arching in the inclined core. Moreover, as the overburden thickness increases, the arching at the bottom of the inclined core becomes more pronounced, leading to a concentrated and regionalized distribution of the arching coefficient that increases the likelihood of local damage.