Negative ion in the air is absolutely necessary to human being just like sunshine. The life of negative ion is very short, it's about a few minutes in clean air and only a few seconds in dirty environment or even shorter. In the open fields, seashores, country, water and spring areas its life can reach to more than 20 minutes, because in these areas the air pressure is smaller and the dust is fewer, so more negative ions can be generated from the air. The World Health Organization advises that the concentration of negative ion in fresh air shouldn't be below 1000~1500pcs/cm 3 . However, due to too many cement road surface, large vehicle flow rate, industrial pollutions and high population density, etc., the concentration of positive ions such as suspending granules, germina and dust, etc., will increase, and the concentration of negative ions will obviously decrease. That can lower the quality of air and affect health level of human body.