The invention discloses a circulating fluidized bed boiler performance calculation method based on calcium balance. The method comprises the following steps of analyzing the content of the calcium element in coal as fired, limestone desulfurizing agent, fly ash and slag, based on the principle that the calcium element is conserved in the whole combustion and desulfurization reaction, the coefficient K for representing the desulfurizing agent and fuel is introduced, a calcium balance basic formula is put forward, then through a chemical equivalent relation and a grey balance formula of fuel inthe boiler and the desulfurization reaction, a correlative iterative computation procedure is built, through iterative calculation, the numerical value of the coefficient K is calculated, and the relative amount of the limestone desulfurizing agent which is put into the boiler to be reacted is determined. Through the analysis method, the situation that the mass and flow of the fuel and desulfurizing agent in the boiler are directly measured is avoided, the test uncertainty is lowered, on the basis of using a conventional method for testing the circulating fluidized bed boiler performance, theboiler thermal efficiency can be more accurately calculated, and the utilization rate of the desulfurizing agent is obtained; meanwhile, the desulfurizing recycling value of pulverized ash can be evaluated.