Abstract: Coal reservoirs have features of low pressure and low permeability, making exploitation difficult andwell yieldlow. However, multi-branch horizontal well may increase the contact area with the coal, enhance production and shorten the economic recovery period. Hence well trajectory optimization criterion of coalbed methane (CBM) multi-branch horizontal well is presented in this paper. In addition, authors established a trajectory optimal design model of the sidetrack horizontal well and then used sequential quadratic programming method (SQP). Finally well trajectory is planed by this model based on geological data in Zhengzhuang of Shanxi Province. The results show that the model achieves optimization design of multi-branch horizontal wells of CBM and deserve somewhat consideration for guideline in the process of well design.