The ground filter must serve the dual function of allowing drainage while preventing particle leakage. With the intensification and changing patterns of rainfall, preventing clogging by sand and gravel is becoming an important issue to maintain drainage performance in earth structures. 3D filters are promising alternatives because the structure can be customized arbitrarily according to the grain size of the original ground. The 3D filter is characterized by the wire diameter (φ), which is the diameter of the mesh forming the lattice, and the pore diameter (d), which defines the space within the lattice. In this study, we focused on the wire diameter of 3D filters with diamond structures and used Discrete Element Method (DEM) analysis to investigate the effect of wire diameter on filter function. It was found 3D filters with thinner wire diameters were able to reduce particle leakage and maintain higher porosity. In the case of the wire diameter less than 2.4 mm, most particles remain static within the filter and leakage tends to be moderate. The optimal wire diameter was estimated to be 1.6 to 2.4 times the D₁₅ particle size, providing an effective balance between drainage capacity and particle runoff protection.