The invention relates to a method for preparing a fibrilia reinforced cellulose ester base composite material, comprising the following steps that: firstly, the fibrilia is converted into fibrofelt after degumming, carding and hot pressing; secondly, cellulose esters and plasticizer are mechanically mixed according to a certain proportion and sealed and balanced for a period at room temperature; thirdly, the fibrofelt is laid in a cellulose ester plasticizer multi-component substrate according to design specification; fourthly, the cellulose ester base composite material is obtained through molding or hot briquetting method. The raw materials used by the method have wide source, can be degraded and regenerated, is reasonable in price, and is safe and nontoxic; the method for preparing thecomposite material is simple and controllable and has good mechanical property and high water resistance; and the mechanical property is obviously improved compared with cellulose ester materials which only use plasticizer. Therefore, the composite material is a novel material which can be degraded completely and have development potential.