Abstract: The cross flow speed in bottom is the main factor to dispose of rock fragment and clean well-bore bottom. This paper established the well - bore bottom plane source - source superposition physical model for cross-flow field of triclinic combination jet flow of tricone bit. Based on hydromechanical basic
principles, point - source scattering physical model in well bore bottom plane with vertical single nozzle jet, and source convergence superposition physical model in well - bore bottom plane incline single nozzle jet, mathematical model was drawn .It includes almost all design about tricone bit having truck with
cross flow field in well bore bottom plane. The calculated results of the cross flow speed and distribution in well - bore bottom plane coincide with field and experiment results, the paper also provides a theoretical support for design of the tricone bit and the hydraulic parameters.

Key words: jet drilling, roller bit, bottom hole, cleaning, flow velocity, flow field, physical model, calculation