Abstract: This article gives a new discussion and a new evaluation method about the three parameters of the Barton equation, according to tests of the shear strength in some laboratories. When the shear strength (, ) of a discontinuity in a jointed rock mass is obtained, the problem how to stimulate three parameters (, JRC , JCS) of the Barton equation should be solved theoretically. But it is impossible to apply the partial derivative equation for solving the problem because of the specialty of the Barton equation. On the basis of discussion of the Barton equation, this article applies the least square method and compiles some programs to solve the problem, and a very good result is gotten.