Soil nutrients systematic evaluation method was adopted to study soil nutrients and effect of potassium on economic character of seed of melon and seed-melon,yield and benefit of seed-melon.Result showed that potassium could improve economic character of seed of melon and seed-melon,which includes single melon weight,melon seeds weight per melon,melon seeds output ratio,one hundred seed weight of melon seeds,kernels output ratio,and lengthwise and sidewise diameter of melon seeds;and that potassium could increase yield of seed-melon,yield of melon seeds with potash was increased by 157~230 kg/hm~2,increase range was from 9.2% to 13.5%,compared to that without potash;and potassium also increases product value and net income of seed-melon,product value and net income of seed-melon with potash respectively increased by 942~1375(yuan/hm~2) and 818~1104 yuan/hm~2,compared to that without potash.Marginal benefit analysis showed that potash dosage that reaches the highest yield and the maximum profit was 135 kg/hm~2.