The expanding incorporation of renewable energy sources has led to a notable rise in the application of grid forming(GFM) converters within power systems. However, in weak grid conditions, poor design of inner loop parameters can lead to severe stability problems in GFM converters. This paper presents inner loop controller design for GFM converters based on D-partition method, providing stability boundary characterization for control parameters that meet multiple performance criteria such as phase margin, gain margin, and short-circuit ratio. This method allows for the quick and accurate determination of inner loop control parameters through graphical visualization, thus eliminating the need for repetitive trial-and-error adjustments. The proposed design method's effectiveness is demonstrated on a 25kW experimental platform.