In heterogeneous wireless networks (HWNs), paths constituting multipath routing are characterized by selfish rationality. Each path's intentions of pursuing individual profits may cause unreasonable competition for limited wireless resources, which leads to the unreliable data transport problem. Therefore, multipath routing optimization is a challenge issue in HWNs. This paper provides a novel approach to study this issue by employing game theory. By taking the utility maximization as the design goal, limited bandwidth resources as the constraint and path reliability as the key metric, a noncooperative stochastic differential game model is constructed for HWNs. With the feedback Nash equilibrium solution, an optimal multipath routing strategy is obtained. Theoretical derivations and simulation results verify the validity of the method present in this paper.