Provided are a method, apparatus and system for determining a path for the fusion of an IP network and an optical transport network. The method comprises: upon the reception of a transmission service request across an optical network domain, distributing, for a transmission service, a virtual link located in an IP network domain and meeting a service requirement; determining a target service layer path, which matches the virtual link, in pre-saved service layer paths, wherein the service layer paths are located in the optical network domain; and sending an activation request for activating the target service layer path to a controller in the optical network domain.