The properties of nuclei belonging to the α-decay chain of superheavy element ~(295)118 have been studied inthe framework of axially deformed relativistic mean field(RMF)theory with the parameter set of NL-Z2 in the blockedBCS approximation.Some ground state properties such as binding energies,deformations,and α-decay energies Q_α havebeen obtained and agree well with those from finite-range droplet model(FRDM).The single-particle spectra of nucleiin ~(295)118 α-decay chain show that the shell gaps present obviously nucleon number dependence.The root-mean-square(rms)radii of proton,neutron and matter distributions change slowly from ~(283)112 to~(295)118 but dramatically from ~(279)110to ~(283)112,which may be due to the subshell closure at Z=110 in ~(279)110.The α-decay half-lives in ~(295)118 decay chainare evaluated by employing the cluster model and the generalized liquid drop mode](GLDM),and the overall agreementis found when they are compared with the known experimental data.The α-decay lifetimes obtained from the clustermodel are slightly larger than those of GLDM ones.Finally,we predict the α-decay half-lives of Z=118,116,114,112isotopes using the cluster model and GLDM,which also indicate these two models can corroborate each other in studieson superheavy nuclei.The results from GLDM are always lower than those obtained from the cluster model. The properties of nuclei belonging to the α-decay chain of superheavy element ~ (295) 118 have been studied inthe framework of axially deformed relativistic mean field (RMF) theory with the parameter set of NL-Z2 in the blockedBCS approximation. properties such as binding energies, deformations, and α-decay energies Q_α havebeen obtained and agree well from finite-range droplet model (FRDM). The single-particle spectra of nuclei ~ (295) 118 α-decay chain show that the shell gaps present obviously nucleon number dependence. The root-mean-square (rms) radii of proton, neutron and matter distributions change slowly from ~ (283) 112 to ~ (295) 118 but dramatically from ~ (279) 110to ~ ) 112, which may be due to the subshell closure at Z = 110 in ~ (279) 110. The α-decay half-lives in ~ (295) 118 decay chainare evaluated by employing the cluster model and the generalized liquid drop mode] (GLDM), and the overall agreementis found when they are compared with the known experimental data The α-decay lifetimes obtained from the clustermodel are slightly larger than those of GLDM ones. Finaally, we predict the α-decay half-lives of Z = 118,116,114,112 isotopes using the cluster model and GLDM, which also include these two models can corroborate each other in studies on superheavy nuclei. The results from GLDM are always lower than those obtained from the cluster model.