Abstract: Firstly, the mechanical model is based on static equilibrium of the soil arch between two piles in pile-slab wall and soil resistance on its two end sections near two piles. The calculation method is developed. Then the shape function of soil arch is derived. Slide plane is ascertained after analysis of the shape function. The calculation formula of earth pressure on slab between two adjacent anti-slide piles is formulated. The formula has several factors acting on the earth pressure. The factors are analyzed. For the same test, the new earth pressure formula is compared with the Rankine method. It is shown that the distance between two adjacent piles is the main factor. Earth pressure increases as the distance increase. At the end, the calculation formula is illustrated with a practical project.