  We develop two methods to estimate the bulk Lorentz factor of X-ray flare
outflow. In the first method the outflow is assumed to be baryonic and is
accelerated by the thermal pressure, for which the final bulk Lorentz factor is
limited by the outflow luminosity as well as the initial radius of the outflow
getting accelerated. Such a method may be applied to a considerable fraction of
flares. The second method, based on the curvature effect interpretation of the
quick decline of the flare, can give a tightly constrained estimate of the bulk
Lorentz factor but can only be applied to a few giant flares. The results
obtained in these two different ways are consistent with each other. The
obtained bulk Lorentz factor (or just upper limit) of the X-ray flare outflows,
ranging from ten to a few hundred, is generally smaller than that of the
Gamma-ray Burst (GRB) outflows.
