Abstract: The 4# mine goaf in GuangxiBeishan mining Co. L td. is large and irregular in the form. The geological structure of surrounding rocks at the goaf is the anticline structure of Shangfu - Kenyue and the fracture of Indo - Chinese epoch and stage of Yanshan. Besides above structure character of the surrounding rocks, The paper further p resents the rock strata boundary and alteration of the marl and reef limestone in the goaf, aswell as the rock physi2 cal and mechanical indexes. Therefore, the paper classifies three engineering geology group s of rock mass. They are marlite, dolomite and reef limestone. The detailed field investigation of surrounding rockswas carried out by the methods of scan line and bulk density to show the comp rehensive condition of rock engineering geology. Based on the field investigation result, the geometrical parameters for the distribution ofmine goaf structural p laneswere ob2 tained using the cluster analysis. Characteristics of geometrical parameters p robabilitywas obtained about the struc2 tures p lanes. The normal distribution function model wasworked out. The 52and 300dip directions of the two p rimary dominant structure p lanes and the 75dip angle of the p rimary dominant structure p lanes. The results show that thismathematicalmodel can effectively stimulate the joint and fissure distribution in the 4# mine goaf.