A complex reinforced concrete structure building including an annex building(length-to-width ratio=1), an office building(length-to-width ratio=2.9) and two residential buildings(length-to-width ratio=1.4) were required to collapse longitudinally by demolition blasting.The office building with large length and width was sheared into two parts step by step from the middle part under the action of gravity by means of delayed blasting between the rows of columns in the annex building.In this case, the center of gravity of the building was easier to move out of the outside of the building.At the same time, high-speed cameras were used to study the failure time and process of the structure and prove the feasibility of this method.When half-second delay detonators were used for the columns, the reasonable delay time between the last row of columns and the adjacent row of columns was about 200~300 ms.The highest point of the incision corresponds to the position of the last row of columns should be weakened by blasting to improve the reliability of collapse.In actual blasting, it was found that it′s necessary to increase the height of the blasting cut of the first exploded building due to the upward shift of the height of the center of gravity after the annex building blasting, and the form of flat cut was adopted.The countermeasures for flying rocks caused by air ejection in the basement were proposed to provide reference for similar blasting projects in the future.