In order to describe the shape of soil arch behind anti-slide piles,numerical simulations were carried out based on plane stain FEA models.Maximum principal compressive stress traces were investigated based on the calculated results and arch axis equations were set up by fitting analysis.The influences of major factors such as pile space,soil and pile-soil interface parameters,load magnitude on the arch shape were analyzed,and the equation with consideration of aforementioned factors was finally obtained.The results show that pile space and the magnitude of pressure on piles are the most notable factors affecting the arch shape.Ratio of span to rise of arch has a quadratic correlation with pile space.Arch effect will bring soil strength into full use as the pile space is 4.46 times of diameter.Arch rise drops as a steep dropping logarithmic function curve with the increase of pressure,which reflects the evolutionary process of arch effect from formation to development and destruction.