With the deepening of human understanding of marine resources and the acceleration of resource development, marine industrial robots have come to be widely used. Robots are not simply a substitute for manual labour, but a personified electronic and mechanical device that combines human and machine strengths. They have both the ability to react quickly and analyse and judge the state of the environment, and the ability of the machine to work continuously for a long time, with high accuracy and resistance to adverse conditions. In industrial machinery, the gravitational field exists in threedimensional space, but if the distribution of the known field is independent of a coordinate, it is simplified to a twodimensional field, which is called a plane scalar field. There are many two-dimensional field problems in the visual positioning system of assembly system. The exact solution can be obtained by using complex function theory to analyse two-dimensional field in complex plane. In this paper, the application of complex function theory in gravitational field is discussed. In the process of cooperative assembly of marine industrial robots, it is necessary to make the correct choice to improve the cooperative assembly method of marine industrial robots, so that the robot industry in China can undergo development and renewal.