Abstract: The diameter of trees is not only an important factor in forest measuration, but also the important basis evaluation for forest tree growth and site quality. The application situation was elaborated about the diameter measurement method of trees in forest investigation and measuration at domestic and aboard. Discussion was made on the principles, structures and measurement errors of measuring instruments represented by tree diameter measurements. At the same time, the advantages and disadvantages of various measurement methods were compared. Accordingly, this paper could provide theoretical reference for improving the measuring accuracy and efficiency of the tree diameter in forest investigation.