The present invention relates to a steam turbine dynamic balance weighting block operation method. The method comprises the steps of firstly, measuring the angular position of a key phase groove, marking the angular position of the key phase groove at the shaft neck of one section positioned closer to the end surface of a bearing, numbering each weighting plane, measuring the angular position of the weighting installation hole of each weighting plane, marking the angular position of the weighting installation hole at the corresponding part on the end surface of the bearing, rotating anticlockwise along the position of the key phase groove according to a calculated weighing angle, respectively marking out the weighing position of each weighing plane at the shaft neck, rotating the shaft neck and weighing the installation hole of a numbered weighting plane when mark lines on the shaft neck and on the end surface of the bearing are numbered the same. In this way, the weighing operation of each weighing plane is respectively completed. The method is ingenious in design and strict in method, wherein the accuracy of the weighting operation is greatly improved.