Abstract: Promoter activity detection is the significant component of the genetic engineering. The research utilizes the gene of green fluorescence protein (GFP ) as reporting gene, and detects the rd29A promoter which regulates gene expression activities among recipient cell. By particle bombardment to transform the epidermis cells of onion, it observes the gene expression of gfp under the fluorescence microscope after culturing 24h, determining the intensity of fluorescence after gfp is expressed under different culturing conditions so as to diagnose its intensity and achieve the quantization purpose. The method is simple, timesaving and dependable, thus it can be used as a kind of effective measuring in detection of promoter activity.