The invention relates to a short-term load predicting method of a 
power grid. The method comprises the steps: step 1, acquiring historical data and pre-treating the data; step2, decomposing the historical load sample data into a plurality of different-frequency sub-sequences by using 
wavelet decomposition; step 3, performing single-
branch reconstruction to each sub-sequence; step 4, dynamically choosing training samples and establishing a neural network predicting model optimized by a vertical and horizontal intersection 
algorithm; step 5, predicting each sub-sequence 24 hours in advance by using the optimal neural network predicting model; and step 6, superposing the predicted value of each sub-sequence to obtain a whole prediction result. The inherent defects of the 
neutral network can be overcome by optimizing BP 
neutral network parameters by a brand-new 
swarm intelligence algorithm, that is, the vertical and horizontal intersection 
algorithm instead of the traditional algorithm; the burr problem caused by the 
impact load 
processing is solved by the 
wavelet decomposition, the precision declining resulting from the removal of the effective load in the burr pre-treatment is solved and the predicted value of the 
hybrid algorithm is more approximate to the actual measured load value.