Abstract: In China, a great number of oil and gas fields are located in high and steep structures and the areas with larger stratigraphic dip, so they are faced with the difficulties of inclination prevention and ROP improvement. The BH-VDT5000 vertical drilling system which is developed independently by CNPC Bohai Drilling Engineering Company Limited has already been applied in many domestic oil and gas fields successfully, but the dropping accident of guide block happens during the particular construction of vertical drilling. In this paper, the force applied on the guide block during the downhole operation was analyzed. It is confirmed that the reason for the dropping accident is that single-hump structure results in contact and friction between the spring pin and the waist hole of guide block when the guide block is in the state of compression while contacting the borehole wall, so that the guide block is worn and fractured. It was proposed to convert the single-hump structure of guide block into the double-hump structure while installing a solid pin in the spring pin and designing damper structures on both sides of the guide block to prevent the spring pin from being taken out in complex working conditions. The modified BH-VDT5000 vertical drilling system was applied practically in the first section (Ø558.8 mm) and the second section (Ø431.8 mm) of Well Keshen 1102 in the pediment structure of Tarim Oilfield, and its application effect is remarkable.