This study overexpressed dihydroxyacetone synthase (DAS) and dihydroxyacetone kinase (DAK) genes,which are two key genes for formaldehyde (HCHO) assimilation in methylotrophic yeasts,in chloroplasts of geranium to obtain transgenic geranium with DAS/DAK HCHO assimilation pathway,The metabolites of wild type and transgenic geranium under liquid H¹³CHO stress were comparatively analyzed by ¹³C-NMR,and the physiological and biochemical indexes of wild type and transgenic geranium under 48 μg·L^-1 gaseous HCHO stress were measured.The results showed that:(1)Under 2 mmol·L^-1 liquid H¹³CHO stress,overexpression of DAS/DAK genes enhanced the role of Calvin cycle during the H¹³CHO metabolism in transgenic geranium,thereby the yield of sugars increased approximately 2.85-fold,and simultaneously changed the original HCHO metabolic pathways of geranium.(2)Under 48 μg·L^-1 gaseous HCHO stress,the contents of H₂O₂,malondialdehyde and protein carbonyl in transgenic geranium leaves were much less than those of wild type.(3)Under environment-polluted gaseous HCHO stress,the absorptive capacity of HCHO and stomata conductance in transgenic geranium leaves remained significantly higher than those of wild type.These results suggest that overexpression of DAS/DAK genes can effectively improve the ability of geranium to purify the environmental-polluted gaseous HCHO.