Abstract: In the drilling construction of deep hole geological core, the traditional drilling tool of same-diameter wireline corer has technical problems of inefficient drilling, narrow tubular annulus, and high defective rate under complex geological environment, restricting the deep hole drilling development. By optimizing the combination of drilling pipe and drilling bit, the authors in this research developed cross-diameter wireline corer drilling tool, and systematically analyzed the mechanical characteristics. The stress distribution and torsional stiffness under different diameter combinations were identified through mechanical modeling and experimental verification, and drilling tool optimization scheme was constructed. The engineering practices of a rare earth mine exploration, shale gas exploration in Sichuan Basin and Pu'er geothermal well in Yunnan Province shows that the cross-diameter drilling tool could bear high torque of 8 000 N·m and drilling pressure of 200 kN, with the maximum drilling depth of 1 500 m. And this cross-diameter drilling tool show good stability under high temperature of 200 ℃ and high pressure of 30 MPa, with the drilling efficiency rising 35% and the core acquisition rate reaching 98%. The research results provide new solutions for technical problems during deep hole geological core drilling, and important practice guidance for improving deep geological exploration efficiency and core collection quality.