A method for determining a routing path includes: receiving a service connection request message, where the service connection request message includes a source node identifier and a sink node identifier; searching for the path with the minimum cost function value between the source node and the sink node on each wavelength plane according to the network topology information that includes wavelength links and logic links as well as the service connection request information, where the cost function value of a logic link is less than that of any wavelength link in the network; selecting the path with the minimum cost function value as a routing path of the current service. A routing path determining unit is disclosed. Therefore, by preferring the logic link and allowing for the impact caused by the available bandwidth and the quantity of wavelength links in the existing logic links onto routing, the bandwidth resources of the network are utilized most efficiently.