In view of a kind of singularity plants with time delays, a new decoupling internal model control method is first proposed based on pseudo-feed-forward decoupling in this paper, which opened up a new study direction for internal model control. A pseudo-feed-forward decoupling is first designed to decouple the system into an open-loop diagonal dominant system. Rather than performing complex and lengthy calculations, this decoupling method is much better for simplifying the design and calculation. Then the diagonal elements of the decoupled plant are used as an internal model to design a multi-loop internal model controller. The proposed method is also verified applicable for non-singular plants. In order to improve control precisions, the diagonal filter is designed with new Luus–Jaakola (NLJ) optimization algorithm. During the optimization process, the integral of absolute error is adopted as an evaluation index. Finally, two industrial processes are taken as the simulation objects to demonstrate the validity and feasibility of the new method. Simulations results illustrate that the proposed strategy not only avoided complicated computations, but also achieved good trade-off between performance and robustness, even when the system model is mismatched.