Abstract: Using Xinjiang "Huang Hou" muskmelon （Cucumis melo L） as material, by adding certain quantity of CaCO₃ to the nursery media, a mixture of peat and prolite, seven types of media with pH5.0, 5.5, 6.0, 6.5, 7.0, 7.5 and 8.0 were built and their effects on the growth and photosynthetic characteristics of muskmelon seedlings studied. The leaf area and dry matter of roots and seedlings per plant, photosynthetic characteristics and root activity were showed changes with media pH from 5.0 to 8.0.If media pH was below 6.0, the ultrastructure of chloroplast had the trend of collision, concentration of chlorophyll was increased, and net value of photosynthetic rate decreased so that the leaf area and dry matter of roots and seedlings per plant fell down. These changes did not come among the treatments with pH from 6.0 to 7.0. With pH of treatments over 7.0, these effluences were also presented but not severe, compared to pH low in 6.0. Therefore, the reasonable range of media pH was 6.0-7.0, and slight alkaline with media pH over 7.0 would not cause physiological obstacle of seedlings. By using CaCO₃ to adjust the media pH, pH from 6.0 to 6.5 was better.