The source term identification of the time-fractional diffusion equation under Robin boundary condition is studied. This problem is ill-posed. Therefore, we apply Landweber iterative regularization method, Fractional Landweber iterative regularization method, TSVD method, combining TSVD method and Fractional Landweber iterative regularization method, respectively. The comparisons of these four methods are given, which can help us select the most effective method. The error estimates between the regularized approximate solutions and the exact solution are given under the a priori and a posteriori regularization parameter choice rules. Finally, numerical examples verify the effectiveness of the methods.