  We treat the mass of a proton as the total static energy which can be
separated into two parts that come from the contribution of quarks and gluons
respectively. We adopt the essential of the bag model of hadron to discuss the
structure of a proton and find that the calculated temperature, proton radius,
the bag constant are compare well with QCD results if a proton is a thermal
equilibrium system of quarks and gluons.
