China's edible salt is the implementation of the national monopoly on the production and sale of products. It is reported that the general qualified salt production process must undergo more than ten times evaporation solarization, in order to remove all the impurities and heavy metals in the salt. Salt farms generally take a graded crystallization method to tanning salt, the concentration of 25 degrees to 27 degrees can be made into a first-class salt, 27 to 28.5 degrees of tanning into the second level of salt, 28.9 to 30 degrees can only be made into a sun food processing salt. Seawater above 30 degrees can only be used as industrial salt or made into agricultural salt. Xuwen County, the state-owned salt field around the farmers through the well penetration of seawater, basically more than 30 degrees; due to the high concentration, so the sun can be a day out of salt.