For the past cost index analysis method of using the same method to calculate all of the index, which is not applicable. Fully compared the calculation method of Paasche and Laspeyres index, and combined with the characteristics of different cost index, determine the appropriate index methodology of comprehensive and sub-cost index, price index, volume index. Finally, combining with a Power Grid Corporation 2008--2014 Transmission and Distribution Engineering Cost Index, a case is studied. The analysis results show that the index calculation methods proposed in this paper can be more accurate to measure the actual situation of the cost fluctuation.