A theoretical investigation of the principles of energy efficiency improvement in coal-fired power plants by removing a portion of the coal moisture content was performed. The relationship between the degree of pre-drying and coal's energy flow rate, boiler efficiency and power auxiliary rate were comprehensively formulized and graphically presented. The performance of the coal pre-drying power plants using coals with different initial moisture content was also discussed. The results showed that, coal's energy flow rate would increase by 0.6-1.5% as 0.1 kg moisture was removed per kg raw coal. The bioler efficiency would increase by 0.4-0.5% and the power auxiliary rate would slightly decrease by similar to 0.2% Eventually, the net efficiency of the power plant could increase in the range of 0.6-0.9%. Economic evaluation showed that the power plant performed more economically compared with the plant without coal pre-drying. This work provides a broadly applicable approach to formulaically revealing the principles of energy efficiency improvement in power plants by coal pre-drying. (C) 2016 Elsevier Ltd. All rights reserved.