The stability of the slope of an open-pit mine is mainly affected by geological structures such as faults and joint of rock mass. In order to identify the distribution characteristics of the rock mass structural, the Reflex ACT III tools were used to unify the core orientation of 4 geotechnical survey holes. However, the proportion of highly reliable core orientation data for each borehole only 8.05-34.29%, due to the rock mass fragmentation and joint development near the contact zone between granite intrusions and sedimentary rocks, which affects the accuracy of core orientation. Therefor, this article took OTV/ATV survey to obtain lithology and structural characteristics, relationships and direction data effectively and improve the accuracy of geological structure information data of core orientation, through high-resolution, continuous and oriented 360° borehole wall images. Based on this, failure mode of the open pit mine was studied by equatorial polar projection theory and dynamic analysis. According to the result, the main failure mode is wedge sliding failure, with a probability of 12.66%-34.99%, followed by plane sliding, with a probability of 3.40%-20.36%, which provides the foundation for open-pit mining slope control.