The slug flow regime in two-phase flow, a transition between the bubbly flow regime and annular flow regime, is investigated experimentally to study its interrelation between the drift velocity and the length of the Taylor bubble. Due to the complicated shape and dynamics of the tail of the bubble and the tiny bubble generation due to the vortex shedding, the measured data of the bubble length has large scattering. By synchronizing the high speed image recording system with the impedance void meter, the drift velocity and the length of the Taylor bubble were measured accurately. The data gave us the results that the model of drift velocity of the bubble is agree well with the experimental data. However, the model for the estimation of the bubble length have large gap with the experimental data. The model of Mishima and Ishii agrees well relatively with the experimental data. A stability criterion is constructed by combining the drift velocity and the Taylor bubble length. It was found that there is a certain region where the Taylor bubble cannot exist due to the fact that buoyancy energy cannot be dissipated by the drag force effectively.