The controlled modification of material properties through doping has garnered significant interest in materials science research. In this paper, employing first principles calculations, we systematically investigate the doping of beryllium (Be) atoms into the biphenylene network (BP) for the first time. Two doping concentrations, 0.04 (minimum) and 0.17 (maximum), along with two distinct substitution sites, are considered, denoted as Bex-BP-Cy (x = 0.04, 0.17; y = 1, 2). Our results reveal that both Bex-BP-Cy (x = 0.04; y = 1, 2) and Bex-BP-C2 (x = 0.17) exhibit favorable thermodynamic stability. At lower concentrations, they retain metallic properties, while at higher concentrations, Bex-BP-C2 (x = 0.17) is a P-type indirect semi-conductor with a narrow band gap of 0.42 eV using PBE functional and a band gap of 1.72 eV with the HSE functional. The mechanical properties of Be-doped BP display notable anisotropy, indicative of excellent mechanical stability. Furthermore, compared to pristine BP, the absorption capacity of Bex-BP-C2 (x = 0.17) along the x direction in the visible region is significantly enhanced. Our study highlights the effective modulation of the electronic, optical, and mechanical properties of BP through Be atom doping, providing a novel strategy for the design of advanced materials.