A tricone rock bit for horizontal wells and hard formation wells includes three head sections and three cones arranged at the lower ends of the head sections, where the supper parts of the three head sections are connected together to form one integrated drill bit body; jet nozzle bosses are arranged between the head sections on the drill bit body; jet nozzles are mounted in nozzle holes of the jet nozzle bosses; gauge cutting elements are arranged on the top rear of the OD of the head sections, forming a gauge surface on the top of the head sections; the front face of the head sections is a ruled surface, inclining backwards at an angle α, and inclining outwards at an angle β. The tricone rock bit has low lateral vibrations, high stability, good effects of bottom hole cleaning and cutting element cooling, long service life and high penetration rate.