In order to explore the effects of Bacillus methylotrophicus agent on cucumber seedling nursing and substrate enzyme activities under high temperature season, and obtain the optimal content, Bonai 526, Jinyou 1 and Xishu-131 were chosen as materials, the effects of different dosages of bacteria agent (0g/plant, 0.25g/plant, 0.50g/plant and 0.75g/plant, labeled as CK,T1, T2 and T3, respectively) on the growth physiological indexes of cucumber seedlings and the substrate enzyme activities in high temperature environment were measured, and the correlation between substrate enzyme activities and growth physiological indexes was analyzed. The results showed that the biomass, root growth rates (except root diameter), seedling index and G value (the growth rate of the daily average dry mass) of three kinds of cucumber seedlings were increased first and then decreased with the increase of the dosage. Compared with CK, T2 treatment significantly improved the seedling indexes of Bonai 526, Jinyou 1 and Xishu-131 by 77.8%, 108.3% and 63.6%, respectively, the G value were significantly improved by 183.3%, 177.8% and 133.3%, respectively, the root length were significantly improved by 105.6%, 72.4% and 75.5%, root surface area were significantly improved by 174.9%, 111.4% and 122.2%, root volume were significantly improved by 212.0%, 137.8% and 156.3%, and root tip number of seedlings were significantly improved by 108.9%, 58.6% and 64.6%, respectively. The root diameter, chlorophyll content and activities of substrate enzyme (including urease, sucrase and catalase) were increased with the increase of the dosage of bacteria agent. It was noteworthy that three kinds of substrate enzyme activities had a significant positive correlation with contents of chlorophyll （P<0.01). In addition, remarkably significant correlation was found between sucrase activity and the indexes of root activity and dry weight （P<0.01). Sucrase and catalase were both significantly correlated with root surface area, root volume and root diameter （P<0.05). In conclusion, taking consideration of growth physiological indexes, seedling quality and substrate enzyme activies, adding Bacillus methylotrophicus agent to the substrate at 0.5g/plant (T2) level was the preferable treatments, the results can provide theoretical support for cucumber seedling raising during summer high temperature period in Guanzhong region of Shaanxi Province.