Structural, electronic, and optical properties of wurtzite BeO under biaxial in-plane strain are investigated using first principles calculations. The present calculations are based on all the electrons' Full-Potential Linearized Augmented Plane Wave plus local orbital (FP-LAPW + lo). The planar strain is introduced to investigate the bonding characteristics, electronic properties, and optical properties of BeO. We observe that BeO is more stable in an h-MgO structure under large tensile strains. Structural, electronic, dielectric, and optical properties of strain-free and strained BeO wurtzite crystal are examined. Our results indicate that the biaxial strains change the bond lengths between Be and O, and we observe a strong correlation between the structural changes accompanying biaxial strains with the electronic structure variations of BeO. The variation in planar strains has a significant impact on the band gap of BeO, which could be proposed as potential candidate for optoelectronic applications.