The theory accuracy evaluation of device combination orbit is the important base of device allocation design and selection of device combination trajectory. The Jacobian matrix of orbit about measuring element is the kernel of the theory accuracy evaluation model of orbit based on error propagation principle. However, it is hard to get the elements’ analytic expression of the Jacobian matrix of complex orbit equation. The theory accuracy evaluation algorithm of device combination trajectory based on numerical differentiation is raised and designed in the paper. By means of constructing numerical queue and calculating Jacobian matrix by numerical differentiation based on spline interpolation, and then the theory accuracy of device combination orbit is obtained. At the last part of the paper, the algorithm is verified to be effective and practical by compared itsJacobian matrix and accuracy value with single position equation’s.