The stress wave non-destructive testing technology was employed to detect and assess the internal defects of 388 garden trees in the Guangming District of Shenzhen. The results indicated that: (1) 79.38% of the trees exhibit hollow trunks, 15.98% have decayed trunks, and only 4.64% have intact trunks. (2) The trunk hollowing levels of roadside trees are primarily concentrated at level II (38.44%), followed by level III (30.61%), level IV (7.14%) and level V (0.34%). The trunk hollowing levels of park trees are predomimantly distributed in the higher concentrated at level III (45.74%), which constitutes a larger proportion, as well as having a significantly greater distribution in Grade IV (20.21%) and Grade V (2.13%) than street trees. (3) More than 80% of trunk decay and hollowing issues occur in trees with Diameter at Breast Height(DBH)≤40 cm, with decay and hollowing are predominantly resulting from external damage to the trunk. (4) Tree species exhibiting severe trunk hollowing and decay, such as Delonix regia, Camphora officinarum, Falcataria falcata, Cinnamomum burmanni, and Ceiba speciosa, are mainly fast-growing tree species. Insufficient planting and management practices are the principal cause of the extensive damage to trunks and the severe issues of decay and hollowing. The findings of this research can provide valuable references and guidance for planning and managing garden tree species throughout the region.