In this paper, an inverse time‐fractional Schrödinger problem of potential‐free field is studied. This problem is ill‐posed; that is, the solution (if it exists) does not depend continuously on the data. Based on an a priori bound condition, the optimal error bound analysis is given. Moreover, a modified kernel method is introduced. The convergence error estimate obtained by this method under the a priori regularization parameter selection rule is optimal, and the convergence error estimate obtained under the a posteriori regularization parameter selection rule is order‐optimal. Finally, some numerical examples are given to illustrate the effectiveness and stability of this method. [ABSTRACT FROM AUTHOR]