In this paper, we solve the geodesic equation in the space of Kähler metrics under the setting of asymptotically locally Euclidean (ALE) Kähler manifolds and establish global \(\mathcal {C}^{1,1}\) regularity of the solution. The solution of the geodesic equation is then related to the uniqueness of scalar-flat ALE metrics. To this end, we study the asymptotic behavior of \(\varepsilon \) -geodesics at spatial infinity. We will prove the convexity of Mabuchi K energy along \(\varepsilon \) -geodesics under the assumption that the Ricci curvature of a reference ALE Kähler metric is non-positive. However, by testing the Ricci curvature of ALE Kähler metrics, we find that on the line bundle \(\mathcal {O}(-k)\) over \(\mathbb {C}\mathbb {P}^{n-1}\) with \(n \ge 2\) and \(k \ne n\) , all ALE Kähler metrics cannot have non-positive (or non-negative) Ricci curvature.