The invention relates to a chitosan/attapulgite composite material, a preparation method thereof, a degraded transformer oil circulating decolorization system comprising the chitosan/attapulgite composite material, and a decolorization process. The preparation method comprises the following steps: S1, dissolving chitosan to obtain a chitosan solution, and dispersing acidified attapulgite into purewater to obtain an attapulgite suspension; S2, adding glycerol into the chitosan solution, and carrying out uniform stirring to obtain a first solution; S3, adding the attapulgite suspension into thefirst solution under a stirring state to obtain a second mixed solution; and S4, forming the second mixed liquid by freezing, and carrying out vacuum freeze drying to obtain the chitosan/attapulgitecomposite material. The chitosan/attapulgite composite material prepared by the method has a stable structure and excellent decolorization and adsorption effects, and the preparation method is simple.