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To overcome the occlusion of satellite signals by dense canopy that invalidates the use of global positioning systems with agricultural machinery, the paper proposed a global positioning method to establish the global positions of forest trees. First, the domain division method of Euclidean distance and a geometric tangent algorithm are used. Then, three-dimensional data consisting of the centre points of tree trunks in the WGS- 84 coordinate system are obtained by performing a spatial coordinate transformation. Subsequently, the laser scanned the newly detected trunks at a time t, and the scanning area was determined. Finally, the global positioning of trees by agricultural machinery was completed under a dense canopy. The results of field experiments showed that the standard deviation of the positioning error of the per plant tree trunk in the X, Y and Z directions of the space rectangular coordinate in the WGS-84 world coordinate system are 0.03 m, 0.04 m and 0.03 m. [ABSTRACT FROM AUTHOR]