Abstract: ‘Summer black’is one of the main grape varieties under shelter cultivation in south China. Due to its triploid nucleus sterility, enlarging fruit is required in production. To discover an effective method, this study compared once-treatment with twice-treatment by applying different formulations at different periods. The results showed that in twice-treatment of‘Summer black’, soaking was conducted with a concentration of GA3 30 mg/L at blooming stage, then GA3 20 mg/L plus CPPU 3.5 mg/L was applied after 15 days. Under this treatment, fruit ear weight could reach 400 g, berry weight was 6.33 g, and total soluble solid content reached 18.4%. In once-treatment, GA3 50 mg/L plus CPPU 2.5 mg/L was applied for soaking 3 days after full blossom, fruit ear weight could reach 400 g, berry weight was 5.56 g, and total soluble solid content was 18.0%.