The invention belongs to the technical field of electric power, and particularly relates to a 500kV transformer substation cost management and control auxiliary evaluation system model construction method based on an LCC idea. The method comprises the steps of constructing a standardized decision matrix; calculating an index weight vector by adopting GAHP; determining an index weighting evaluationmatrix; solving a positive ideal scheme and a negative ideal scheme according to the TOPSIS; calculating the distance between the evaluation object and the optimal scheme and the worst scheme; calculating the close degree between the evaluation object and the optimal scheme; applying a GAHP-TOPSIS combination method to calculate an evaluation value of each scheme by using a TOPSIS combination method. The method has high practical application value and solid theoretical basis for the cost control of the 500kV transformer substation, has sufficient certified support, provides reference and reference for the cost control research of the power transmission and transformation construction project, and has remarkable popularization significance. The method is suitable for national 500kV transformer substation cost management and control work, and 500kV transformer substation cost management and control can be rapidly and accurately measured from the perspective of the whole life cycle.