  We consider the formation of singularities along the Calabi flow with the
assumption of the uniform Sobolev constant. In particular, on K\"ahler surface
we show that any "maximal bubble" has to be a scalar flat ALE K\"ahler metric.
In some certain classes on toric Fano surface, the Sobolev constant is a priori
bounded along the Calabi flow with small Calabi energy. Also we can show in
certain case no maximal bubble can form along the flow, it follows that the
curvature tensor is uniformly bounded and the flow exists for all time and
converges to an extremal metric subsequently. To illustrate our results more
clearly, we focus on an example on CP^2 blown up three points at generic
position. Our result also implies existence of constant scalar curvature
metrics on CP^2 blown up three points at generic position in the K\"ahler
classes where the exceptional divisors have the same area.
