The anisotropic geometric, electronic, and thermoelectric (TE) properties of bulk BP with strain applied along three lattice directions have been systematically investigated using first-principles calculations combined with semi-classical Boltzmann transport theory.It is found that the lattice constant b always increase whatever compressive or tensile strain is applied along z direction, showing an unusual mechanical response with a transition between positive and negative Poissons ratio, which may due to the hinge-like structure of BP.The electronic properties of BP are sensitive to strain that there exist transitions of band gap among direct, indirect and zero with strain varying from tensile to compressive, indicating that invoking strain is an effective way-to modulate the electronic structure of BP, which may have potential applications in nano-electronics.For the TE performance of BP, when there is no strain applied, the ZT value is found to be maximal along x direction as 0.722 at 800K with an electron (n-type) doping concentration of 6.005×1019cm-3, while being smaller for hole (p-type) doping or along other directions, indicating a distinctly anisotropic TE performance.Furthermore, the greatest enhanced ZT values could be obtained for electron (n-type) doped BP as 0.866 at 800K with a tensile strain of 7% applied along y direction, promising the potential of BP as a new TE material for future applications, which would also be helpful for raising the comprehension of phosphorenes properties.