In deep mineral resources exploration, more and more boreholes with depth of more than 500m are used, and the deviation becomes increasingly prominent. Based on the inclination survey data from a fluorite ore, the analysis is made on the causes of borehole deviation from the geological conditions and drilling construction technology, the analysis is indicated that there is still some regularities to follow. The special wheel effect is the basic reason which leads drilling azimuth deviation to the rotation direction; the special geologic structure and improper construction technologies are the main factors which cause abnormal drilling deviation. Therefore, the prevention measures must be prepared in geological design and construction process.