Abstract: This paper builds an artificial bee colony cellular automata (CA_ABC) model with Nanjing as the study area, calibrates CA_ABC model by simulating urban expansion from 2000 to 2007, and validates the CA_ABC model from 2007 to 2015 using the actual land-use data. End-state overall accuracies (OA) are 80.61% for 2007 and 87.79% for 2015, while figure-of-merit (FOM) metrics are 19.25% for 2007 and 21.23% for 2015. This paper uses CA_ABC and Markov chain calculating the total urban land amount in Nanjing in 2025 and 2035, predicts the land-use pattern and analyzes the urban encroachment on ecological land. The prediction results show that urban expansion will mainly come at the expense of cultivated land and forest land in the next 20 years. 80% of the urban expansion in 2025 and 2035 will come from the encroachment on cultivated land, and 17% of the urban expansion area is the encroachment on forest land in 2015. This study shows that accurate simulating and predicting the future urban pattern and evaluating the urban encroachment on ecological land are helpful for decision makers reasonably plan for sustainable urban development.

Key words: cellular automata, artificial bee colony, land use, urban encroachment, Urban CA, Nanjing city