In view of the problems such as rough calculation， large errors in the results of the traditional security check on power grid dispatching planning， an auto-generation method of the day-ahead forecast power flow based on multiple data sources is proposed， which can generate the day-ahead forecast power flow automatically and improve the precision and accuracy of security check on power grid dispatching planning. First， proceeding from the day-ahead forecast power flow calculation model， an analysis is made of the parameter constitution in the normal operation mode of day-head power grid. Then， by means of parameter acquisition and parameter fitting from multiple data sources， various parameters for use in the day-ahead forecast power flow calculation are automatically generated to preliminarily form the model for the day-ahead forecast power flow calculation. Finally， the model of power flow is adjusted according to the combined dynamic power flow algorithm to automatically generate the convergent day-head forecast power flow. Application of the dispatching planning security check system in Lanzhou power grid has verified the convergence and effectiveness of the proposed method.