The experiments for Q235-A steel using the Tianjin JG-2016 numerical control YAG laser processing machine showed that the laser working voltage, laser pulse frequency, laser pulse width and assistant gas pressure influence the round degree mostly among all the laser drilling parameters. Based on the mode of Grey relevant analysis in grey system theory, the rule relation among the laser drilling parameters which effected the round degree and conical degree was fomid, and a building up mixed mathematical models using grey system GM (1,N) model and neural network model was also proposed which can reflect the nonlinear and multi-coupling relationship of the laser drilling surface round degree, conical degree and laser drilling parameter. Thus the processing technology of the laser drilling can be optimized, so as to improve the qualities and reduce the round degree and axial conical degree error as well.