In this paper, we study the following fractional Schrödinger equation with electromagnetic fields and critical or supercritical growth \(\begin{aligned} (-\Delta )_A^su+V(x)u=\lambda |u|^{p-2}u+ f(x,|u|^2)u, \ x \in \mathbb {R}^N, \end{aligned}\) where \((-\Delta )_A^s\) is the fractional magnetic operator with \(0<s<1\) , \(N>2s\) , \(2_s^*=\frac{2N}{N-2s}\) , \(\lambda >0\) , \(V \in C(\mathbb {R}^N,\mathbb {R})\) and \(A \in C(\mathbb {R}^N, \mathbb {R}^N)\) are the electric and magnetic potentials, respectively. When V and f are asymptotically periodic in x, and f is a continuous function and there exists \(2< q<2_s^*\) such that \(|f(x,t)|\le C(1+|t|^{\frac{q-2}{2}})\) for all (x, t), for \( 2_s^*\le p<22^{*}_{s}-q\) . For any \(D>0\) fixed, if \(\lambda \in (0,D]\) we prove that the equation has a nontrivial solution by the truncation method. Our method can provide a prior \(L^{\infty }\) -estimate.