For the purpose of analyzing the stability of walking mobile excavator, which moving cross direction on the sloping ground, a static model including multi-degree system for working mechanism and chassis mechanism was described, and the additional inertia moment of working device during its rotating was also considered. A mathematical model of multi-objective optimization for the stability of walking mobile excavator was constructed. The utility function method was employed to solve the optimal model. The maximum degree of slope and state parameters of working mechanism and the chassis were optimized. The results showed that the proposed method has its merits, such as simple and reliable, and it could provide theoretical basis for confirming the cross direction moving parameters of the walking mobile excavators and safety controlling.