Inter-satellite optical communications can meet the needs of large-capacity transmission of satellite communications. The space-wide optical networks based on WDM intersatellite links (ISLs) and wavelength routing technology is an important approach to solve low-latency, large-capacity transmission and low-power on-orbit real-time routing process. And routing and wavelength assignment are its key technologies. For RWA problem, this paper takes the typical 2π constellation NeLS and π constellation Iridium constellation as examples, and proposes a method to determine the optimal inter-satellite link topology, and establishes a simulation model of two typical constellation routing strategies and wavelength requirements. The results show that the small-scale Iridium constellation has the characteristics of faster RWA algorithm, better connectivity of network topology nodes and lower demand for wavelength resources. The large-scale NeLS constellation of satellites can reduce the wavelength requirement of the link arbitrary optical networks through increasing the physical connectivity or reducing the maximum allowable hops.