This paper takes the aerial treepruning robot that is used for clearing the tree barricades near highvoltage lines as study object, and the attitude control problem of the aerial robot is addressed. Firstly, the attitude dynamics model and control allocation matrix of the aerial treepruning robot with new structure are established. Then, in order to overcome the uncertainty of the inertia matrix, the sliding mode method is used to design the attitude controller. At the same time, a nonlinear function is introduced to improve the traditional boundary layer method and enhance the controller performance. Then, a control allocation matrix switching strategy is proposed to solve the dynamics model change problem of the aerial robot in the cutting operation process. Finally, the controller was implemented on the simulation platform. The experiment results show that the sliding mode controller designed in this paper has good attitude control performance and can effectively overcome the inertia uncertainty of the robot body. Through switching the control allocation matrix, the attitude stabilization of the aerial robot in the cutting operation process is realized.