As part of the 6th mobile communication, satellite networks are developing rapidly. Advantages of low latency, high capacity of low earth orbit (LEO) satellite constellation are recognized through role of Starlink in Russo-Ukrainian War and commercial use of satellite networks such as Starlink and Oneweb. However, for low orbit altitude and small area coverage of LEO satellite, little constellation information is obtained by a single LEO satellite, resulting in difficulty of producing a global optimal routing algorithm by a single LEO satellite. In contrast, geostationary (GEO) constellation constructed by 3 GEO satellites covering much larger area by a single GEO satellite, relatively stationary to earth, usually with more powerful processing ability, can share GEO constellation information more efficiently. Based on feature of LEO and GEO constellation, a congestion avoidance routing algorithm for GEO-LEO two-layer satellite network is proposed in the paper, in which GEO satellites gather queue length information from LEO satellites and send global queue length array to LEO satellites, enabling production of a global optimal routing algorithm for every LEO satellite.