To analyze the resistance mechanism of apple to Glomerella leaf spot, we analyzed 87 cultivars (lines) including ‘Gala’, ‘Mato’ and their F₁ individuals in this study. The field investigation, artificial inoculation, pathogen biomass detection, and SSR molecular marker identification were used to analyze the differences in resistance to Glomerella leaf spot in different varieties (or lines). The difference in salicylic acid resistance related genes, the defensive enzyme gene expression level, and the defensive enzyme activity were detected by the realtime fluorescent quantitative PCR and the enzyme activity methods. The results showed that: (1) there were significant differences among 87 cultivars (lines) in resistance to Glomerella leaf spot. ‘Gala’, ‘25’, ‘1919’ etc. had severe leaf disease phenotype and showed high susceptibility to Glomerella leaf spot. ‘Mato’, ‘409’ and ‘1616’ etc. had no or very few leaf spots. The content of pathogen biomass was significantly lower than that of susceptible varieties (lines). (2) The accuracy of SSR markers S0405127 and S0304673 genotypes was 93.10% and 91.95%, 91.95% and 95.40%, respectively, compared with field phenotypic investigation results and artificial inoculation results. (3) The expression patterns of SA related genes showed that MdEDS1, MdPAD4 and MdPAL were strongly induced in resistant varieties (lines) such as ‘Mato’, ‘409’ and ‘1616’ after inoculated for 4 days. Furthermore, the expression level of SA signal transduction related genes MdNPR1, MdPR1 and MdPR5 was significantly higher than those in susceptible varieties (lines) such as ‘Gala’. (4) After inoculated the pathogen for 4 days, the expression level of MdSOD and MdPOD and enzyme activities in ‘Mato’, ‘409’ and ‘1616’ and other resistant varieties (lines) were significantly higher than those in susceptible varieties (lines) such as ‘Gala’, ‘25’ and ‘1919’. These results preliminarily showed that salicylic acid synthesis, signal transduction pathway and oxidationreduction reactions process were involved in the resistance of ‘Mato’, ‘409’ and ‘1616’ and other resistant varieties to Glomerella leaf spot. This research provided important guiding significance for mining resistant genes and breeding resistant varieties by using desirable germplasm resources.