The mechanism of soil arching effect is important for anti-slide pile design. With the 2D particle flow method (PFC2D), the forming and failure process of the soil arching between anti-slide piles are simulated. The results show that the forming mechanism of soil arching mainly depended on stress transit process of micro soil granule. In the anti-slide pile numerical models (PFC2D), the contact stress transit trace lines present the tree crown shape, which centered about the anti-slide pile. The load from far field is transited to the front and side part of piles through the compress soil. When the soil between anti-slide piles collapses, the failure surface presented the arching shape. The cross-section and spacing of anti-slide piles affect the soil arching shape strongly. With the same pile spacing and soil parameters, the ultimate bearing capacity of rectangular cross-section pile is larger than the circle cross-section pile.