Given the increasing demand for energy and the rising cost of fossil fuels, the development of nuclear fission and fusion reactors has become a key priority. Recently, High Entropy Alloys (HEAs) and Medium Entropy Alloys (MEAs) have emerged as promising materials for use in nuclear reactors due to their unique properties, which include significant lattice distortion, high configurational entropy, reduced diffusivity, and the cocktail effect. In this study, we designed and analysed a series of FeCrV-based Refractory Medium-entropy Alloys (RMEAs) as structural materials in fusion reactors, using Density Functional Theory. By calculating the empirical parameters, we have verified the solid solution's structure stability of the FeCrV-based RMEA. We examined the mechanical, electronic, and irradiation resistance properties of these alloys and found that the incorporation of tungsten dopants could enhance both the mechanical properties and irradiation resistance of the materials, with the optimal doping level being approximately 8% of Tungsten. Furthermore, electronic structure calculations were performed to elucidate the underlying mechanisms. This knowledge can guide the development of new HEA/MEA materials for use in nuclear reactors.