Abstract: The model of operational availability (A₀) was established based on Markov process theory under two levels of support. It was difficult to select the design parameters directly because of the complex model. Thus, the calculation of searching for optimum result with the help of optimum method was needed. Genetic algorithm was employed to study this problem. The optimal solution of A₀ and the corresponding parameters were obtained in the reasonable range of λ, μ, σ₁ and σ₂. Calculation results can provide guidance for the design of A₀ to a certain extent.