The on-load capacity regulating transformer can really realize the automatic regulation of transformers capacity during the operation process with load， and can reduce no-load power losses of the transformer effectively. The structure characteristics and the energy-saving operation principles of on-load capacity regulating transformer are described. The configuration of the automatic control system and the main functional blocks for implementation of on-load adjustment of transformers capacity， are introduced. By analyzing the transformers economic operation mode and its critical economic capacity， the typical reference value of switchover position for its economic operation is given. The design and the implementation methods for the key control strategies， such as economic operation strategies and secure operation strategies， are described. The operating effects and the economic benefits of the on-load capacity regulating transformer developed are followed and analyzed， and the future application is prospected.