Identification of urban growth patterns is essential to better understand urbanization and its eco-environmental consequences. Landscape indices, such as the simple urban growth index (S) and the landscape expansion index (LEI), are commonly used to identify urban growth patterns, but most of them are unable or not robust enough to recognize multi-temporal patterns. In this study, we proposed the modified urban growth index (Sm) with a 4-step approach and identified the urban growth patterns of three fast growing cities, namely, Xishuangbanna, Phnom Penh and Ho Chi Minh City. The results of Sm and S in identifying multi-temporal urban growth patterns were compared, and the multi-temporal outlying patches were always classified as edge-expansion patches or infilling patches in the results of S. Based on Sm, the spatial and temporal changes of urban growth patterns in the case cities were presented. Generally, Sm performed better in identifying multi-temporal urban growth patterns than S. However, like many other indices, it has limitations in certain situations. We further discussed the potential applications of urban growth pattern identification using Sm. First, the identified multi-temporal urban growth patterns validated the diffusion-coalescence theory. Outlying patches usually tended to decrease during the transition period from diffusion to coalescence, while edge-expansion growth and infilling growth always became dominant urban growth patterns at the end of the coalescence process. The dynamics of urban spatial structure could also be recognized by highlighting the multi-temporal growth of outlying clusters. In conclusion, with the identification of multi-temporal urban growth patterns, the modified urban growth index Sm is able to delineate the diffusion-coalescence process of urban growth and reveal the evolving characteristics of urban spatial structure.