The invention discloses a medium and long term power load forecasting method based on a factor-main attribute model. The medium and long term power load forecasting method based on the factor-main attribute model includes that step 1, building (n-1) impact factor indexes X1-Xn-1 and an original matrix of a forecast object Xn, using Z standardization to pre-process the impact factor index data X1-Xn-1 and Xn, and carrying out dimensionless on the index data to obtain an index matrix Ao*n; step 2, according to a factor analyzing method, confirming a selected common factor, calculating the corresponding factor score, and building a factor forecasting model FORMULA (shown in the description); step 3, sieving to obtain main attributes m1, ..., mr according to a main attribute algorithm, wherein the main attribute model is FORMULA (shown in the description), and v is the feature vector; step 4, building a factor-main attribute medium and long term power load forecasting model according to FORMULA (shown in the description), calculating to obtain a normalized forecast variable value, performing Z standardization formula conversion, and calculating again to obtain the practical value of the corresponding original variable value.