The theoretical accuracy evaluation of device combination trajectories is a critical foundation for device allocation design and trajectory selection. Existing models for accuracy evaluation are based on the error propagation principle, using the Jacobian matrix of the trajectory with respect to measurement elements as their core. However, obtaining the analytic expressions for the Jacobian matrix elements in complex trajectory equations is challenging. This paper proposes and designs a theoretical accuracy evaluation algorithm for device combination trajectories based on numerical differentiation. By constructing numerical sequences and calculating the Jacobian matrix using numerical differentiation with spline interpolation, the theoretical accuracy of the device combination trajectory is determined. The algorithm’s effectiveness and practicality are validated by comparing the Jacobian matrix and accuracy values of the proposed method with those derived from a single device position equation.