Generally, leafy vegetables planted in winter and spring cover the shading net directly on the surface of leafy vegetables (floating surface cover) to prevent low temperature hazards. Because of its light weight, it is only about 45 grams per square meter. Does not overwhelm, buckle, or degrade commodity properties. And because it has a certain permeability, the surface of the leaves is still dry after covering, which reduces the occurrence of disease. It also has a certain degree of light transmission, and it will not “cover yellow and cover badly” after covering. In 1997, Henan Agricultural University in the Lintang County Longtang Vegetable Park, the winter greenhouse celery which has been basically grown, was covered with a floating surface in the shed for cold protection. No icing was found in the leaves of celery; while those in single-layer sheds, especially the upper and middle leaves, had been frozen and hardened, and it was determined that the covered ones were 1.5 ℃ higher than the control temperature.