Abstract: By applying the auxin phenylacetic acid (PAA) in tobacco haploid plantlet leaf vein tissue somatic culture,the action and mechanism of avtive carbon and different category of the carbonhydrate effect PAA used in leaf vein tissue culture one-step seedling formation of tobacco haploid plantlet was researched.The results showed that maltose is not the sole carbon source prompting PAA one-step seedling formation success, the glucose have the same effect with the maltose.After adding activated carbon, sucrose may also promote the occurrence of PAA one-step seedling formation.the reason was proved by the experiment that sucrose will be decomposed into fructose and glucose in the condition of high-press- -killing-bacterium.And, in the same condition, fructose can be decomposed into 5-hydroxymethyl furfural (HMF).HMF is an inhibitor of one-step seedling formation which can be absorbed by avtive carbon.The experiments show that the effect of PAA stimulating one-step seedling formation appears to depend on the category of the carbonhydrate and active carbon.