In this paper,on researching of joint face distribution distances,the appearing possibility of different dimensions of block was analyzed. Many random factors were taken into account when calculating the block reliability,such as angles of joint face,binding force,friction coefficient,the rock density,etc. The analysis process has been compiled into program and can be used for analyzing the appearing and failure probability of different dimensions of block on the excavating space of stone engineering construction. The analysis result can provide scientific basis for anchoring and sparging concrete design.