Pb, Hg and Cd will affect human health by vegetative chain. In recent years, people more and more are concerned about heavy metal pollution of the soil-plant system. Many researchers studied the effect of single heavy metal on growth, photosynthesis, respiration and quality of plants, but few systematicstudies of the effect of heavy metals on the scavenging system of activated oxygen of plants. This note systematically studies the effect of Pb, Hg and Cd in soil on the scavenging system of activated oxygen in tobacco leaves. 1 Material and methods Material: Tobacco (Nicoticana tabacum L). Methods: Cultivating and measuring methods were according to reference. 2 Results Results of this study indicate that the common effect of Pb, Hg and Cd on activity of CAT is obvi- Pb, Hg and Cd will affect human health by vegetative chain. In recent years, people more and more are concerned about heavy metal pollution of the soil-plant system. Many researchers studied the effect of single heavy metal on growth, photosynthesis, respiration and quality of plants, but few systematic stains of the effect of heavy metals on the scavenging system of activated oxygen of plants. This note systematically studies the effect of Pb, Hg and Cd in soil on the scavenging system of activated oxygen in tobacco leaves. and methods Material: Tobacco (Nicoticana tabacum L). Methods: Cultivating and measuring methods were according to reference. 2 Results Results of this study indicate that the common effect of Pb, Hg and Cd on activity of CAT is obvi-