Herringbone horizontal well can increase bare area and output of coalbed methane reservoir. The design calculation is separately made in single awaiting drilling trajectory and main well bore trajectory, the separated well bore trajectory can be transformed into 2D trajectory for design. The optimization design model of multi-branch horizontal well bore trajectory was established according to the characteristics of herringbone multi-branch horizontal well and analysis was made on the relationship between multi-branch well bore and main well bore. The result shows that the distance and the angle between branch well and main well are in direct proportion with depth and dogleg; under the condition of fixed angle between branch well and main well, dogleg is in inverse proportion with depth.