To improve the accuracy and quality of consumer daily power data in system database, a real time on-line method for modification of consumer power data is proposed. The method combines the improved extrapolation and secondary modification based on the least square method to quickly modify the power data on-line and store it in the database. Firstly, the method obtains the longitudinal changes and the corresponding weighting factor by extracting the similar daily electricity data of the current date and then combined with the lateral changes of the current power data to modify the power data. Finally, the least square method is used for the secondary modification of the power data which conforms to the principle of the secondary modification. The daily power data of a consumer in Wuhan is adopted to validate the effectiveness of the method and the results show that the quality of power data is improved to a certain extent.