Typhoon is one of the most important and frequent natural factors that disturbs the green space ecosystem of coastal cities. Super Typhoon Mangkhut hit Shenzhen with a maximum onshore gust of 46.5 m/s (category 15) in September 2018. This study explored the impact of this typhoon on trees in the urban green space (parks, residential neighborhoods, and street trees) in Shenzhen based on field investigation right after the disaster, using statistical methods and biomass assessment. The results showed that (1) the damage rate of trees in the urban area of Shenzhen was up to 21.4%, among which the main damage was mild damage (i.e., branches broken), and the total canopy biomass decreased by 8.44%. (2) Spatially, the extent of damage was significantly higher in coastal area than in the interior, and in the southeast than in the northwest. Futian, Longgang and Pingshan district suffered the most serious damage, with the proportion of damaged trees exceeding 30%. The canopy biomass loss in the central and eastern regions was higher than that in the western regions. (3) The damage was the worst in parks, and the least in residential neighborhoods. (4) The damage rates of Ficus microcarpa and Cassia fistula were both more than 50%, while that of palmae was slight. These results can provide insights for selecting wind-resistance trees and designing disaster reduction and prevention strategies for urban green space of different types in Shenzhen.