The present invention relates to pharmaceutical and medical technologies, and more particularly to novel nanobodies against pulmonary surfactant protein A (SP-A) and their preparation methods. The nanobodies of the present invention comprises an amino acid sequence having certain formula. The present invention also relates to nucleic acid sequences encoding the nanobodies, their preparation method and their applications. Immunohistochemistry and in vivo imaging show that the nanobodies of the present inventions have high lung-targeting specificity.