Abstract: With the continuous expansion of the hybrid scale of AC/DC transmission projects, the working conditions of the bridge arm reactors are becoming more and more complex. The existing designs can not meet the needs of complex working conditions, and one single design constraint is difficult to achieve comprehensive performance optimization.Under the development trend of diversified engineering needs, it is necessary to take all design indexes into account.In this paper, an equivalent electromagnetic model under AC/DC composite working conditions is proposed. Based on the structural parameters obtained at the power frequency, the encapsulation currents of the other frequencies are solved, and the actual overload and harmonic conditions are considered in the calculation; Based on the weight coefficient, a hybrid constraint design methodology is proposed, and the constraints of the combination of encapsulation current density, the resistance voltage and the temperature rise are formed. A weight coefficient adjustment strategy is proposed, meanwhile, an objective function is established to quantitatively compare different design cases. On these basis, facing the actual harsh demands of the reactor, three other objective functions are constructed, clarifying the optimization process and optimizing the encapsulation structure by using the gradient descent method. For the example of an ±800kV bridge arm reactor, the hybrid constraint design methodology reaches a 'compromise' among all indexes, the effectiveness of the design methodology verified by a series of tests of the prototype.