The study of network supported opinion dynamics in large groups of autonomous agents is attracting an increasing interest during the last years. In this paper, we proposed the use of the recent graphon theory to model and simulate an interacting system describing the evolution of individual opinions over an arbitrary size networks. Specifically, we prove the existence and uniqueness of the limit problem that approximates a very large networks made by homogeneous groups of agents. The significant new example is the mean field analysis deduced from the graphon limit systems in the case of piecewise constant graphon.