Abstract: Multi-lateral horizontal CBM wells can effectively increase the drainage area, reduce the skin factor and remarkably increase production capacity. In order to obtain the most cost-effective production capacity, the optimization of such wells’ wellbore structure is essential. This paper investigates the effects of coal seam dip angle, reservoir protection and wellbore structure on the productivity of horizontal CBM well. Taking a multi-lateral horizontal CBM well in 3# coal seam for block of the southern Qinshui basin, as an example, numerical simulation is conducted to optimize the parameters of the wellbore structure. It turned out that, the orientation of main hole had great impact on production capacity, with the most preferable orientation as perpendicular to the direction of main permeability; the production capacity increased with the lengths of main hole and laterals, which taking the economy and enhancement effecs should be controlled in 900~1 300 m and 250~400 m respectively; the spacing between laterals and the angle between main hold and lateral also impair the production capacity to some extent, which should be controlled in 200~300 m and 36°~53° respectively. The research results will provide reference for designing the wellbore structure of CBM multi-lateral horizontal well.