In the transmission line inspection operation, the flying robotic arm with good maneuverability can replace the manpower to complete a variety of scenes that are in danger or difficult to reach by manpower for grasping operations. In this paper, based on the D-H matrix, the tandem robotic arm is initially modeled, combined with the Lagrange equation and the characteristics of the robotic arm, to construct the robotic arm dynamics model. Construct the visual servo frame of the flying robotic arm and define the coordinate system of the visual servo system. Get the center point of the grasping frame by grasping the target, establish the camera coordinate system, and realize the position-based visual servo control. Drawing on the predatory action of the bald eagle in biology, set the grasping strategy of the flying robotic arm. Verify the application effect of visual servo in UAV robotic arm grasping through simulation experiments. The random motion speed of the UAV in three-dimensional space is analyzed, and the maximum speeds of roll, pitch and yaw of the target in the motion process are about 1.311 rad/s, 0.825 rad/s, and 1.239 rad/s. In the estimation accuracy of the flying robotic arm's position, the overlap between the true value of the UAV's position and the trajectory of the estimation value is high, and the x-axis only appears smaller errors in 15s, 26s, and 32s, respectively, at 15s, 26s and 32s. There is a small error of 0.013, 0.003, 0.002m, respectively, and the model has a high accuracy in estimating the position of the UAV.