The basic coordinating model and correlative coordinating model are effective tools to solve the coordinating problem of multilevel load forecasting. The characteristics of the multilevel coordinating model for load forecasting are analyzed. The optimization model of least-squares credibility with constraints is proposed to avoid the possible excessive adjustment phenomenon under the credibility of weighted least squares. Under this optimized combination of credibility， the accuracy of load forecasting can effectively be improved. The mechanism of improving the forecasting accuracy for the multilevel coordinating model based on least-squares credibility with constraints is discussed. In conclusion， a numerical example is given to validate the effectiveness of the least-squares credibility with constraints and to illustrate its effect on the accuracy improvement of multilevel load forecasting.