The fiber placement angle is an important parameter in composite layer design. Different trajectory planning algorithms may lead to the deviation of trajectory angle from the design angle. In this paper, the fixed angle algorithm and geodesic algorithm are compared and analyzed in terms of the direction and paving property of trajectory. On this basis, the theoretical placement angle deviation of composite automatic fiber placement trajectory is studied. Then, a geometric algorithm for calculating the theoretical placement angle deviation is proposed. Furthermore, based on Visual Studio 2010 Platform, CATIA secondary development technology is applied to realize the calculation of theoretical placement angle deviation. Finally, the feasibility, reliability, practicability and efficiency of the algorithm are verified by calculating the laying angle deviation of 45°geodesic trajectory on the truncated composite conical shell.