Abstract: Relative conducity and chlorothyll content of the invasive weed Ipomoea cairica herbaceous companion species such as Polygonum chinense,Bidens pilosa,Oxalis corymbosa and Paederia scandens were mensurated in five different habitats by using the conductivity method and photometric method,and the blank comparison experiment was designed to analyze the above species being without I.cairica.The results showed that there was significant correlation between all companion species and uncompanion species of I.cairica at 0.01 or 0.05 level for chlorothyll content,change of relative conductivity wasn’t distinct among three herbaceous companion species besides B.pilosa,which suggested that reducing chlorophyll content was one of the important mechanisms that I.cairica effected its herbaceous companion species,such as Polygonum chinense,O.corymbosa and Paederia scandens,otherwise,the effect mechanisms of I.cairica included reducing chlorothyll content and increasing membranous permeability to B.pilosa.