National Integrate Circuit Research Program of China [2009ZX02023-003]; National Key Basic Research Program of China [2010CB934300, 2011CBA00602, 2011CB932800]; National Natural Science Foundation of China [60906004, 60906003, 61006087, 61076121]; Science and Technology Council of Shanghai [1052nm07000]; Supercomputing Center, CNIC, CAS ; By means of ab initio molecular dynamics calculations, we have studied the local structures of liquid and amorphous Si3Sb2Te3. The results show that all the constitute elements in liquid Si3Sb2Te3 are octahedrally coordinated. While in amorphous state, Sb and Te atoms are mainly octahedrally coordinated and Si atoms are mainly tetrahedrally coordinated. In both states, Si is mainly homo-bonded by Si. Finally, we proposed a phase separation model for liquid and amorphous Si3Sb2Te3, which is responsible for the good performance of Si3Sb2Te3 alloy as a phase change material. (C) 2011 Elsevier Ltd. All rights reserved.