In the generation and measurement of attosecond pulse using a few cycle laser pulse, the absolute phase of the laser pulse has been an important factor. The relation between the generation of attosecond pulse and the laser oscillation and how the absolute phase affects this relation are discussed. According to our calculation, the random of the absolute phase will not destroy the stability between the attosecond pulse and the laser oscillation. This result supports the direct measurement of the duration of the attosecond pulse with cross-correlation technique theoretically and gives an exact explanation for the experiment result in Ref.