Abstarct: Cadmium selenide (CdSe) is one of group semiconductors compound.It crystalized in two forms, Wertzite and Zinc belend structures.The Bandgap of this compound is direct type and its bandgap in wertzite and zinc blende phases are about 1.797 eV and 1.712 eV respectivly. In this study the electronic structure and optical properties of pure, doped with Be and Zn elements in zinc blende phase and its Nanosheet structure have been investigated. Calculations of pure and Nanosheet structures are performed by using both GGA and LDA approximation and for doped samples calculations were performed by using GGA approximation. Calculations are done using Pseudopotentiol approach and extended plane wave and by Quantum Espresso package. In study of electronic structure of the samples, band structure, total and partial density of states were calculated. For study of optical properties, the dielectric function, refractive and extinction coefficients, reflectivity, absorption coefficient, optical conductivity and energy loss function were calculated. Investigation of the density of states of pure cadmium selenide shows that the area above the valence band (near the Fermi level) arise from hybridization of s and p states, of Cd atom and p state of Se atom. Conduction band minimum also arises from hybridization of s and p orbitals of Cd and Se atoms. Results of calculation show that doping cadmium selenide with Be and Zn dopants (that replace Cd atoms), increases the band gap of the samples. The bandgap also increases with increasing of dopand concentration. This phenomenon occurs because of Burstein-Moss effect. The calculated band structure of cadmium selenide indicates that this material in the form of nanosheet is also a direct band gap semiconductor. The obtained band gap is about 1 eV. The calculated density of states of the nanosheet show that the area above the valence band is mainly due to hybridization of s, p, d orbitals of Cd atoms and p orbitals of Se atoms. The conduction band minimum is also the result of hybridization of s, p states of Se and Cd atoms. The caculated imaginary part of the dielectric function shows that the absorption edge is shiffted toward higher energies in both dopant atoms with increasing dopant concentration. Optical properties of CdSe nanosheets due to quantum confinement effect undergo many changes. Absorption edge of CdSe nanosheets displaced toward higher energies.