The present invention relates to a method of improving soybean transformation efficiency, which comprises: transforming a plant cell using a recombinant vector containing a gene of interest and a gene encoding a sulfonylurea herbicide hydrolase; screening and culturing the transformed plant cell by external application of an ALS inhibitor, using the gene encoding the sulfonylurea herbicide hydrolase as a selective marker; selecting a plant cell that has not been killed and/or not been inhibited. The present invention firstly proposes that a selective agent is added to a proliferation medium and a differentiation medium in a manner of external application during plant transformation process, and optimizes the effective screening concentration range of the selective agent, so the transformation efficiency is remarkably increased, and the proportion of positive plants obtained in the progeny thereof is significantly increased; at the same time, the transgenic plants obtained by the transformation using the sulfonylurea herbicide hydrolase gene as a selective marker in the present invention have high commercial value, good resistance and genetic stability.