Abstract: According to the drilling technology characteristics of directional horizontal grouting well and stratum characteristics of limestone layer, the characteristics of stratum to be drilled, drilling technology and conventional bit wear are studied, by analyzing the geological characteristics and structure of site, borehole design and well body structure. The bit profile shape, cutter arrangement, cutter mounting Angle and diamond composite were optimized. Parabolic profile, Limit density distribution of teeth and increasing reserve teeth for key parts to reduce the bit key parts wear and tear, improve bit offensive, and through the numerical simulation analysis of rock fragmentation efficiency of special-shaped cutter, and strengthen the cutting teeth of nose , improve bit impact toughness, prevent bit impact damage. The service life of the optimized bit is increased by 58.18% compared with conventional PDC bit in field test. The average speed of composite drilling is 50% higher than that of conventional PDC bit. The average speed of directional drilling is 56.52% higher than conventional PDC bit, which achieves the requirements of optimal and fast drilling for bottom grouting construction in limestone layer, and provides a bit design scheme for directional well drilling in hard rock fractured stratum, and provides technical support for the construction of grouting well in similar stratum.