The algorithm to derive the transfer functions of 2-D continuous-discrete systems has been presented. The given 2-D system with arbitrary order and arbitrary topology structure can be analyzed. We construct the algorithm by nodal equations, 2-D Laplace-z transformation, 2-D signal flow graph. Resorting to the algorithm, we develop computer aid analysis software for deriving the transfer function of a 2-D continuous-discrete system. An example for analyzing a 2-D lattice continuous-discrete system shows our algorithm to be valid.