A new 2D monolayer namely penta-BeP2 carried out by the density functional theory is reported. Our simulations indicate that the 2D penta-BeP2 shows good structural, dynamical and thermal stabilities as demonstrated by cohesive energy calculation, phonon dispersion simulation, and molecular dynamic analysis respectively. It is discovered that the penta-BeP2 is a 2D semiconductor with a strain tunable indirect band gap of about 0.8 eV computed by HSE06 level of theory. Analyzing the optical behaviors of this monolayer shows the monolayer has visible light sensitivity suggests its promising application in optical devices for using in low energy range of electromagnetic spectrum.