Abstract: Research on host plants invaded by pathogenic fungi have great significance in plant disease. Solophenyl flavine 7GFE can attach to hyphae, which give fluorescence under 330-380 nm light. This paper modified a fluorescence staining method using solophenyl flavine 7GFE to observe fungal hyphae invading plants. Results showed that the most suitable leaf staining condition was 0.002% (M/V) solophenyl flavine 7GFE dissolved in 0.1 mol/L Tris-HCl (pH 8.5) for 5 min. Using 95% ethanol instead of 0.15% trichloroacetic acid (W/V) alcohol solution:chloroform (V/V) 4:1 for decolorization and omission of safranine staining simplified operation and reduced toxicity. The modified staining method was used to observe potato leaves invaded by Phytophthora infestans and achieved good effects. The modified staining method was fast, effective and non-toxic, and was suitable for observation of the invasion process of fungal pathogens and hosts.