We investigate the above-threshold ionization of an atom in a combined infrared (IR) and extreme ultraviolet (XUV) two-color laser field and focus on the role of XUV field in the high-order above-threshold ionization (HATI)process.It is demonstrated that,in stark contrast to previous studies,the XUV laser may play a significant role in atomic HATI process,and in particular,the XUV laser can accelerate the ionized electron in a quantized way during the collision between the electron and its parent ion.This process cannot be explained by the classical three-step model.Our results indicate that the previously well-established concept that HATI is an elastic recollision process is broken down.