Abstract: A way to construct a clean combustor with high performance and low contamination is proposed by means of installation with beforehand mixing and evaporating.Direct measurement or accurate calculation of the evaporation rate in the evaporation installation is very difficult. According to energy relation,calculation is made based on the quasi steady state evaporation model at the angle of engineering use.The concept of greatest evaporation rate of fuel in the evaporating installation is presented,and the effect of some primary factors is analysed.The calculated results are compared with test data.