A human granulocyte colony-stimulating factor (hG-CSF) gene was synthesized and inserted into a trp expression vector for overexpression in E. coli. A strong expression vector was constructed, and a simple purification procedure including in vitro refolding was estabilished. The final productivity of hG-CSF was 500 similar to 600mg per l culture, and the purified hG-CSF showed the proliferation of neutrophils in vivo assays.