The effects of Sn added in CoCrFeNiSn_x (x = 0.05, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1) high entropy alloy on the corrosion behaviors in 3.5 wt.% NaCl aeration aqueous solution and the mechanical properties have been investigation. During the dynamic polarization tests, the metal ion concentrations at several applied potentials were detected by ICP-MS for the performance of corrosion resistance. The surface morphology and the composition of each phase before and after corrosion tests were observed and analyzed by SEM/EDS. The related crystal structure of each phase was further investigated by TEM and XRD. The as-cast specimen after annealed at 1050℃ for 48 h has revealed the only one phase of FCC CoCrFeNiSn_z at x ≦ 0.05, while the second phase of orthorhombic Ni_(3-y)(CoCrFe)_ySn₂ high entropy intermetallic compound has been found increasing with x increasing at x ≧ 0.1, also leading to the increasing hardness. Meanwhile, the content of Ni decreases and those of Cr and Fe increases with x increasing in FCC CoCrFeNiSn_z matrix. Since the pitting always happens and proceeds on the FCC phase area and the Ksp of Ni(OH)₂ is much greater than those of Cr(OH)₃, Fe(OH)₂ and SnO₂, the corrosion resistance also increase with the increasing content of Sn. Due to the high contents of Cr, Fe and Co existing in Ni_(3-y)(CoCrFe)_ySn₂, the smaller sized particles of CoCrFeNiSn_z FCC and Cr-Fe-Co rich BCC phases further precipitate after annealed. On the other hand, the supersaturated Sn content in the original FCC CoCrFeNiSn_z is forced to precipitate the finer orthorhombic Ni_(3-y)(CoCrFe)_ySn₂ particles. Besides, both lattice parameters of FCC and orthorhombic phases increase with the content of Sn increasing. The passivation films composed of hydroxyl mono-layers on CoCrFeNiSn_z and Ni_(3-y)(CoCrFe)_ySn₂ are also simulated by the first principle based on density function theory for corresponding to corrosion behaviors.