Abstarct: In this work, we instigated the structural, electronic and magnetic properties of pure ZnSe and doped with transition mextals elements. The calculation was performed using liner approximation plane wave plus local orbitals method baxsed on density functional theory frxame work by WIEN2k package. First the structure and electronic properties of pure ZnSe were studied using two approximations PBEsol- GGA and LDA and also the phase change of the ZnSe from the Zinc blend to the Rock Salt investigated under applied pressure. Then the structure, electronic and magnetic properties of ZnSe doped by transition elements were studied by GGA(08) approximation. In this stage the effects of transition elements on band structure and density of states were investigated. The results of calculation show the structure of ZnSe changes from the Zinc blend structure to the rock salt structure with increase in pressure. Comparing the calculated ground state energies of different magnetic phases in Fe, Co and Ni doped samples; show that the stable magnetic phase is the ferromagnetic for Fe and Ni and anti-ferromagnetic for Co. The results of band structure calculation indicate that the band gap is directed in the ferromagnetic phase and reduces compared to pure sample due to the overlap of the Se: p orbital and the d orbital of impurity atoms. Ferromagnetic phase in Fe and Ni doped samples in percentage of 6.25, 12.5 and 25 and Co doped at percentage of 6.25 is half-mextal but in 12.5 and 25 percentages of Co doped samples are semiconductor.