Abstract: By means of proton beam irradiation，two water melon[Citrullus lanatus（Thunb.）Mansfeld]inbred lines Q29541 with early maturity and promising quality and R87345 with crisp flesh and tough peel were developed and used as maternal and paternal parents to produce hybrid watermelon cultivar Tangshan 3. The duration of fruit development in this cultivar was 29 to 31 d. The first pistillate flower was present at 8 to 10 nodes on the main volubile stem and also in an interval of 3 to 5 nodes. The red-colored sarcocarp was crisp. The sugar contents of the center and the side were 12% and 9%，respectively. The weight per melon was over 6 kg. This cultivar has demonstrated a broad adaptability and good perspective of commercialization based on 5-year demonstration in 14 provinces，for example Hebei，Liaoning，Tianjin，Anhui，Hubei，He’nan，and Shandong.

Key words: watermelon, proton beam, cultivar