The invention discloses a surrounding rock reinforcement technology of a city underground excavation section downwards traversing existing buildings. The surrounding rock reinforcement technology includes the following steps that before a soil body of the pre underground excavation section is excavated, an advance grouting support measure is adopted by the arc crown of the pre-excavation cross section and the outer side of the contour line of a side wall; after the soil body of the underground excavation section is excavated, and a preliminary support measure is adopted by the arc crown of theexcavation cross section and the side wall part. The purpose of the surrounding rock reinforcement technology is that for the problem, existing in an existing underground excavation technology, thata support measure is not adopted by the side wall part of the excavation cross section, the surrounding rock reinforcement technology of the city underground excavation section downwards traversing the existing buildings is provided. According to the construction technology, the cross section side wall part is supported, and stability of the stratum around the excavation cross section can be obviously improved.