Abstract: With muskmelon (cucumis melo L.cvs) Huanghou as the material, the effects of concentration of nutrient solution on the growth and photosynthetic characteristics of muskmelon seedling were studied. The results showed that high concentration of nutrient solution induced the accumulation of salt in the root zone and its EC value reached 0.8 (mS/cm) when the concentration of nutrient solution was higher than 2.0 (mS/cm). When the concentration was higher than 2.0 (mS/cm), there was a salt toxic symptom in the cell's ultrastructure. The cytoplasm became hollow inside and the chloroplast was swelling with a global shape which was partly grided. Cell walls were sunken and there was a separation between the cytoplasm and its cell wall. When EC was higher than 2.5 (mS/cm), these symptoms became much more (severe.) The reaction of the net photosynthetic rate of muskmelon leaves was same as roots. Before 12 a.m, the net photosynthetic rate was increased with the increase of concentration of nutrient solution, but after 12.a.m, it decreased with the increase in the value of EC, especially when EC was over 2.0 mS/cm. When EC got over 2.5 (mS/cm,) it decreased more. However, leaf area per seedling and chlorophyll concentration showed a positive correlation with the increase of concentration of nutrient solution, Therefore, we concluded that the concentration of solution should not be higher than 2.0 mS/cm, and EC should be kept within a range between 1.5 and 2.0 mS/cm.