Side initiation is a common initiation method in rock blasting. Reasonable initiation methods have an important influence on rock fragmentation. In this study, the explosion energy-transmission process under the side-initiation method is analyzed. The rock-fragmentation result of side initiation and end initiation are compared with transition material blasting excavation field tests in the Changhe Dam. The results from this theoretical analysis and the field tests show significant differences in the partition of shock and gas energy between different initiation methods. In view of energy transmission, compared with end initiation, shock energy can be converted to gas energy, which results in a reduction in shock energy and an increase in gas energy. In addition, the side-initiation method is suitable for blasting in soft and fissured rocks and for contour blasting. It is unwise to use side initiation in the blasting of hard and compact rocks because it will reduce the proportion of shock energy.