Mechanical head-end processing of SF disassembly, extraction of the rods, the cutting of the extracted rods and the slitting of cut rods shall be performed in advance as the head-end process of the pyro-process that can recycle the light water reactor spent fuel (SF). For the operation and maintenance of the Pyro head-end process, the digital mock-up verification on design of the horizontal slitting systems (slitter) for spent fuel rods is required. Also, the horizontal slitting main device with remote ability should be optimized for maintenance. For this, modularization and pre-verification of the horizontal slitting main device were conducted with solid works simulation tools. Also, the characteristics were analyzed and modularized reflecting the requirements for the horizontal slitting main device and 3D modeling was carried out using Solid Works tool. The digital mock-up verifications of the horizontal slitting main device were conducted to enhance the remote control efficiency. The above analysis results can be utilized in the head-end process design of the SF dry process through a concept design of the horizontal slitting system for the spent fuel rods.