Micro grinding with a poly crystalline diamond (PCD) tool is one of the promising approaches for fabricating a micro mold on difficult-to-cut materials. As the process can also achieve good surface integrity without additional finishing processes, it could shorten total processing time and reduce total energy and resource impact. Modeling of micro grinding is necessary to understand the key design factors of the PCD tool which influence the grinding force inducing geometric errors in micromachining. This research proposes a model to describe the micro grinding of the difficult-to-cut material and predict the grinding force. The model for calculating the grinding force has been established considering contact area, grit size and distribution, tool shape, cutting depth, and cutting speed. Micromachining experiments with a PCD micro grinding tool fabricated by wire electro discharge machining have been conducted in tungsten carbide and provided the validation of the proposed model.