‘Xinshengdai No.3’is a new triploid seedless watermelon F₁ hybrid developed by crossing tetraploid line‘TS-3’as female parent with diploid line‘Q-7-5’as male parent. It is of mid-maturity. The whole growth period is about 105 days. Its fruit development period is 33-35 days. It grows vigorously. Its leaf blade is of medium size. The plant can set fruit easily. The fruit is round with dark black and shining peel. The average single fruit weight is about 7.0 kg. It can yield about 45 t·hm^-2. The flesh is red with fine texture. The fruit is crispy with sweet flavor and good quality. The central soluble solids content is 11.58%. Its peel is 1.2 cm thick. It is tolerant to storage and transportation. This cultivar is suitable for cultivation in all parts of China.