Based on the cycling function method

and starting from the algorithm of power generation rate from thermalization and of the saved coal amount from heat-and-electricity co-generation

the relationship between power generation rate from thermalization and saved coal amout from heat-and-electricity co-generation has been expounded.Analysis shows that the saved coal amount from heat-and-electricity co-generation is relating to the external power generation rate from thermalization

as well as the ratio between internal and external power generation rate from thermalization

however

it is mainly determined by the external power generation rate from thermalization

the bigger the external power generation rate from thermalization is

the better economic efficiency of the thermal power plant becomes;in the event of certain external power generation rate from thermalization

the greater ratio of internal to external power generation rate from thermalization is

the better economic efficiency of a thermal power plant becomes.The above-mentioned conclusions have already been verified through concrete examples of calculation.