Abstract: The soil arching effect in the passive zone between the internal pit and external foundation pit was analysed based on the stress and deformation features of supporting structure. A formula of passive soil pressure is established by using the theory of soil arching effect when the supporting structure of the external pit rotates around the bottom. A conception of the relative displacement ratio is put forward to describe the change of earth pressure in the external pit when the structure of the internal pit has displacement. The calculated earth pressure is nonlinear. The calculation results of engineering example prove that the method in this research could better reflect the impact of soil arching effect and pit-to-pit distance on earth pressure than classical methods. It also shows that this new method is safer than Coulomb’s earth theory when designing the supporting structures. When there is no displacement of the internal pit supporting, the smaller distance between two pits, the bigger relative displacement ratio of supporting structures and the bigger passive earth pressure will be, which means that improving the interior supporting stiffness is beneficial to controlling the deformation of the external pit supporting.