The complex structure demonstrated here was a two stage G T interferometers,who not only has the same periodical nature as single stage G T interference,but also improves dispersion capacity by limiting light reflected inside the cavity.This structure was used for multi channel dispersion compensation simultaneously,especially for tunable dispersion compensation.According to the calculation,one more reflection between these G T cavities could increase dispersion capacity of complex G T interferometer by a certain amount.Due to this principle,dispersion tunability could be realized by controlling the reflection time between complex cavities.Although the dispersion properties of such devices will be degraded by a couple of factors,such as unconformity of cavity length and unparallel of the G T cavities,the structure of dual cavity G T interferometer could be finely designed for multi channel dispersion compensation.