The creep damage evolution of asphalt binder plays a significant role in investigating the formation mechanism of rutting, a common type of distress at high temperature for asphalt pavements. However, the reliability of existing creep damage parameters is under questioned, and these parameters cannot accurately illustrate change law of intrinsic microstructure about asphalt binder. In this paper, a new testing protocol is given access to study the evolution of viscoelastic parameters during creep damage. It is completed by inserting the frequency sweep during creep test. The frequency sweep curve clusters are fitted using the generalized Kelvin-Voigt model for obtaining the change law of model parameters. Based on the change law and sensitivity analysis of model parameters, (E2 + E3)/2 is proposed as the creep damage variable. According to the curve of (E2+E3)/2 versus loading time, two stages during the creep test can be identified: an approximate constant value in phase Ⅰ and a linear decrease in phase Ⅱ. Intrinsic differences about creep property of binders can be determined by this new proposed parameter. Above results not only ensure better understanding of the creep damage mechanism of binders, but also lay the theoretical foundation on predicting the anti-rutting performance of binders.