Tree barrier is an important cause of line trip and even blackout of power grid. It is of great significance to study the partial discharge mechanism of the conductor near the tree for the early warning and prevention of tree barrier. The partial discharge test platform of the conductor near the tree is set up. The high-frequency discharge current

power frequency voltage

and ultraviolet as well as visible images of the test circuit are comprehensively monitored. The influence of environmental humidity

crown shape and moisture on the discharge characteristics are studied. The research results show that the discharge form and development process of tree-conductor are closely related to such factors as the moisture of trees and the speed of wires near the trees. And the discharge has such three forms as direct breakdown flashover

intense discharge without arcing and stable arcing without flashover. For the latter two kinds of discharge forms

the pre-discharge current at the average amplitude up to 40～500 mA

the wave head time at0.17～0.88 μs and the wave tail time at 1.42～6.81 μs can be generated. The conclusion of the study lays a theoretical foundation for the monitoring and early warning of the discharge of the actual transmission lines near the trees.