Despite significant advantages over analog counterparts, digital controllers for switching DC-DC converters demand the use of different tools such as MATLAB/SIMULINK and Verilog-AMS to model and simulate the design. As a consequence, this inevitably complicates the design procedure. A novel approach is therefore proposed to simplify the process. By using the GUI-based tool developed, the controller for digitally controlled buck converter can be automatically designed and implemented with Verilog HDL under a unique and consistent MATLAB/SIMULINK environment. Verification results of both system-level and mixed-level models are given to show the validity of the proposed design approach.