The selection of soil rupture surface is related to the calculation accuracy and engineering economy in the stability analysis of retaining structure，sometimes it also affects the engineering safety. Considering that the rupture surface of foundation soil may be located inside the sheet pile cellular when it overturns，we analyze its failure mode and calculation method，build a numerical model to analyze the location of soil rupture surface at the bottom of the sheet pile cellular based on an engineering example，propose the calculation assumption of“double rupture surfaces”of Hansen method in view of the inconsistency of the bottom elevation of adjacent cellular，give a specific calculation example，and propose two methods to improve the stability of soil failure surface inside the cellular. The results show that increasing the penetration depth of sheet piles and strengthening the soil in the passive area and inside the cellular can effectively improve the stability of sheet pile cellular along the internal failure surface.