We consider a fractional Adams method for solving the nonlinear fractional differential equation C 0 D α t y(t) = f (t, y(t)), α > 0, equipped with the initial conditions y (k) Here, α may be an arbitrary positive number and α denotes the smallest integer no less than α and the differential operator is the Caputo derivative. Under the assumption 2004) introduced a fractional Adams method with the uniform meshes t n = T (n/N), n = 0, 1, 2, . . . , N and proved that this method has the optimal convergence order uniformly in t n , that is, the optimal convergence order of this method cannot be obtained with the uniform meshes. However, it is well-known that for y ∈ C m [0, T ] for some m ∈ N and 0 < α < m, the Caputo fractional derivative C 0 D α t y(t) takes the form " C 0 D α t y(t) = ct α −α + smoother terms" (Diethelm et al. Numer. Algor. 36, 2004), which implies that C 0 D α t y behaves as t α −α which is not in C 2 [0, T ]. By using the graded meshes t n = T (n/N) r , n = 0, 1, 2, . . . , N with some suitable r > 1, we show that the optimal convergence order of this method can be recovered uniformly in t n even if C 0 D α t y behaves as