Watermelon breeding included two main components，that was inbred lines selection and heterosis utilization.The similarities and differences of watermelon inbred breeding and hybrid varieties were described.The effects of four main factors on watermelon heterosis were analyzed,the selection principal which were clearly matching the principle of hybrid parents target character，their parent quality traits or pairs,cumulative target quantitative trait gene of the parents,and use a high general combining ability parents cvene stated.