Using the similar material and simulating test sample joints by prepared vitriol sheet, the sacle effect on compressive strength of five kinds of fractal distribution joints rock mass is studied by test and numerical simulation, in which the uniaxial compressive strength of the small-scale test sample is obtained form the test, and the the unaxial compressive strength of the large-scale test sample obtained by computer simulation by testing conditions. On the base of analyzing the strength change with the scale or the joints distribution dimension, the planar empirical equation is put forward. It is concluded that the rock ductility law increasing with the number augument of rock masses joints is deduced, however, the damage process and way are controlled by the joints distribution.