Autoregressive conditional heteroscedasticity (ARCH) models , which broke though the assumption of constant variance of traditional econometrics , have had a profound influence to the modern capital asset pricing theo2 ry. Along with development in researching time-varying variance , variance persistence has being concerned by more and more economists. In this paper we firstly introduce the conceptions and the properties of conditional mean , con2 ditional variance and the persistence of autoregressive conditional heteroscedasticity models , and then discuss the capital asset pricing model of a portfolio which follows the time-varying conditional variance process. Moreover , in the end of the paper , we analyze the persistence of multi-asset portfolio which follow a vector GARCH process