Most large commercial aircraft engines are hanged below wings. When the aircraft makes an emergent landing process, at the same time, the landing gear cannot work or the centrifugal force becomes unbalanced as the fan blades fly away. In order to ensure safe landing, overall tank crack and fuel leak should be avoid at the crack area. Access to a large number of emergent landing accidents, emergency break-away is essential. In this paper, the break-away position, which locates between the pylon and the wing, is mainly considered. We choose true size in the models of wing, pylon and engine. High strength steel is employed for the bolts which connect pylon and wing. Earth and lake are employed concrete and pure water respectively. SPH method is applied in the case that the aircraft lands on the lake. Whats more, different landing cases have been analyzed. By constantly adjusting the size of pins, a set of conclusions of the emergent landing problem are obtained in the simulation process. The locus of centroid of engine and pylon is obtained, and then the condition which may achieve safe flight and avoid the secondary damage to wings can be chosen, from which we can provide reasonable designing strength of the wing box and accordingly provide reference for the design of aircraft structure.