The present disclosure is appropriate for the technical field of packaging bag materials, and provides a full biodegradable high-barrier multi-layer composite material and a preparation method thereof as well as a packaging bag. The full biodegradable high-barrier multi-layer composite material comprises the following components: polylactic acid, terephthalic acid-adipic acid-butanediol copolyester, polyvinyl alcohol, polyurethane glue and starch carrageenan. Embodiments of the present disclosure provide the full biodegradable high-barrier multi-layer composite material which is obtained by using the terephthalic acid-adipic acid-butanediol copolyester as a degradable layer, using polyvinyl alcohol as a barrier layer and by composing the degradable layer with the barrier layer via polyurethane glue and starch carrageenan. Through the present disclosure, the problems, such as high oxygen permeation rate, poor barrier property and poor preservation degree, in the existing degraded film can be solved.