This paper presents an optimization study of the stability of the top beam of a two-leg shield hydraulic support based on the theory of force equilibrium zone. The work aims to avoid the structural damage caused by the “flak” or bow of the top beam. Firstly, the area of the support force equilibrium zone and the load-bearing capacity of the column bearing zone are viewed as the performance indicators and their varying tendencies with the increase of the ratio of the top beam and the working position of balance ram are analyzed. Secondly, with the ratio of the top beam and the location dimensions as design variables, a multi-objective optimization model is established by taking the sum of weighted performance indicators as objective function. The optimization problem is solved by using genetic algorithm to obtain the optimal design variables correspondent to the strongest stability of the top beam. Finally, the force equilibrium zones of the hydraulic support and loadings of the balance ram before and after optimization are compared. The result shows that through the optimization of the top beam ratio and the location dimensions of the balance ram, the stability of the top beam is improved significantly and the stress of the balance ram is effectively reduced, leading to the reduction of the possibility of structural instability caused by the damage of balance ram and/or its connection ears.