Abstract: This angle gauge method was first proposed in 1948 by the Austrian forester Dr. Walter Bitterlich.Since then the method has been adopted in forest mensuration work in many countries and won wide acclaim for its simplicity and general efficiency. This article gives an account of some results growing out of our studies on the method. These include: First,to present the method in a way somewhat different from the ordinary,the authors make an effort to approach its basic principle and theory from a mathematical point of view,hoping that this will help those who employ the method in their work operate more efficiently. Second,the use of an ordinary simple angle gauge has been restricted to basal area enumeration in the past.Now,a method for estimating the number of trees per unit area of a forest stand,is described,and it proves workable with pretty high efficiency by tests in the field.In combination with this,the technique of determining the mean dia- meter of a stand is developed. Third,the idea of extension of the original angle-gauge principle to the direct estima- tion of the mean height of a stand was first introduced by T.Hirata of Japan.But so far as yet the problem of estimating mean height on slopes has not been completely solved. In this article,a method specially designed for the purpose is derived.This new method turns out to be not only sound in theory,but also simple enough for operation in practice.