In the fields of aerospace, energy equipment, and shipbuilding, the application of robot milling is becoming increasingly widespread. However, predicting milling force and dynamic deformation still poses challenges. Existing models handle cutting force and robot dynamics separately, failing to reveal the complex interactions between milling force and deformation under position-dependent stiffness variations. Therefore, this paper considers the influence of the robot’s dynamic deviation on the tool position and posture, establishes a tool tip motion model, and proposes a milling force prediction method that takes into account the effects of tool position and posture deviations. Additionally, by combining the changes in the robot’s dynamic parameters at different postures and time points, an iterative dynamic modeling and time-domain solution method for force-position coupling suitable for robot milling is developed. The effectiveness and accuracy of this model have been verified through synchronous monitoring data of milling force and processing deformation. Experiments show that this method can capture the influence of milling force dynamic deformation and achieve precise prediction of instantaneous cutting load (radial milling force error ≤ 10%). In terms of processing deformation prediction, a step-by-step integration scheme is used to calculate the end effector deviation under the changing dynamic parameters over time, with simulation errors below 8%. The proposed model and solution can be integrated into the Cyber-Physical Production System (CPPS) to enhance the intelligence level of robot milling processes.