Abstract： The demolition blasting of the tailrace outlet cofferdam of Baihetan hydropower station has obvious characteristics of tight construction schedule，heavy task，complex rock conditions，close proximity to protective objects and high requirements for slag washing by water flow． In view of the important and difficult points in the construction，a phased，partitioned and layered blasting demolition scheme was adopted，and thus the single cofferdam was divided into two phases，three layers and eight zones． By reserving an economic cofferdam and demolishing the part above water in advance，the difficulties of huge engineering quantity and tight construction schedule were overcome． The method of drilling with large-diameter drills and protecting the hole with casing effectively reduced the occurrence of hole collapse under complex geological conditions，improved the construction efficiency and ensured the blasting effect． The design of high powder factor，low single shot，inter-hole segmentation and intra-hole delay not only met the requirements of safety control of vibration velocity，but also ensured that the rock fragmentation after blasting can be washed away by water flow． The engineering application results showed that the peak vibration velocity of blasting under the most unfavorable conditions was 11． 85 cm/s，which was less than the allowable safety control standard of 12 cm/s for structural concrete． The measured peak pressure of surge wave was 0． 12 MPa，which was also under the allowable value of 0． 4 MPa for hydraulic steel gates． The fragmentation after blasting was controlled mostly within 40 cm，and the boulder yield was controlled within 5%． The research results can provide reference for similar projects．