Abstract: In order to prevent gas hazards, thousands of upward cross-seam boreholes for gas pre-drainage are widely used in underground coal mines. Their construction quality directly determines whether coal gas accidents happen and touches miners’ lives closely. However, the quality is difficult to be guaranteed, because of the hostile underground environment, complicated spatial calculation, sightless strata reserves and little digitalized supporting. Based on the vector algebra theory, a novel algorithm is proposed which abstracts boreholes as a set of vectors and calculates their parameters step by step. The algorithm consists of three parts that are borehole path calculation, the computation of boreholes group distribution and additional boreholes designing. Then an algorithm-based design and simulation software system is developed which follows a strict logical flow and implements five functions, namely importing basic data, the 1st designing, storing construction data, rendering virtual scene and appending additional boreholes. At last, through application case in Qinan coal mine, the system is proved to be objective, effective and helpful to simplify design effort and improve visualization.