This paper presents one on-line model for energy efficiency calculation and analysis. The computation model of combustion rate and other related physical and chemical equations were introduced to the heat balance computing model of boiler. It established one on-line model of thermal process, which can provide the functional relationship completely in real-time measurable variables to the calculation of energy efficiency. And on that basis, the theory on deviation analysis was introduced to establish the model for energy efficiency quantitative analysis to calculate the single-factor distributed consuming difference. The situation of the CG-220/9.81-M boiler’s energy efficiency was calculated and analyzed with the diagnosis model. The calculation errors of thermodynamic parameters related and the errors between the lumped energy efficiency deviation and the sum of single-factor distributed efficiency deviation were both small. The model is reasonably accurate. The on-line model for energy efficiency diagnosis of thermal power pulverized coal boiler was established.