We propose a method to improve the secret key rate of an eight-state continuous-variable quantum key distribution(CVQKD)by using a linear optics cloning machine(LOCM).In the proposed scheme,an LOCM is exploited to compensate for the imperfections of Bobs apparatus,so that the generated secret key rate of the eight-state protocol could be well enhanced.We investigate the security of our proposed protocol in a finite-size scenario so as to further approach the practical value of a secret key rate.Numeric simulation shows that the LOCM with reasonable tuning gain λ and transmittance τ can effectively improve the secret key rate of eight-state CVQKD in both an asymptotic limit and a finite-size regime.Furthermore,we obtain the tightest bound of the secure distance by taking the finite-size effect into account,which is more practical than that obtained in the asymptotic limit.