NOVELTY - Decoloration of biodiesel prepared from waste oil includes pretreating; catalyzing by solid acid; and decoloring crude diesel. The step of decoloring crude diesel includes flowing the crude diesel treated by solid acid to diesel decoloring tank from an intermediate tank; blending and raising temperature; adding alkaline decoloring agent; raising temperature; decoloring; filtering; obtaining light yellow biodiesel; and transferring the light yellow biodiesel to biodiesel finished product tank. The alkaline decoloring agent is prepared by mixing sodium-based bentonite with sodium carbonate.    USE - Decoloration of biodiesel prepared from waste oil (claimed).    ADVANTAGE - The method achieves good decoloring effect without using water washing step, thus, saving water resource; and avoids environmental pollution.    DETAILED DESCRIPTION - Decoloration of biodiesel prepared from waste oil includes pretreating; catalyzing by solid acid; and decoloring crude diesel. The step of decoloring crude diesel includes flowing the crude diesel treated by solid acid to diesel decoloring tank from an intermediate tank; blending and raising temperature to 55-65 degrees C; adding alkaline decoloring agent (4-6 wt.% based on the weight of crude diesel); raising temperature to 100-110 degrees C within 15-25 minutes; decoloring for 15-25 minutes; filtering; obtaining light yellow biodiesel; and transferring the light yellow biodiesel to biodiesel finished product tank. The alkaline decoloring agent is prepared by using sodium-based bentonite as raw material; mixing sodium-based bentonite with sodium carbonate (0.4-0.6 wt.% based on the weight of sodium-based bentonite); at 100-110 degrees C, drying for 20-40 minutes; milling to 180-220 mesh; obtaining alkaline decoloring agent; transferring the alkaline decoloring agent with 180-220 mesh into a drying device with temperature of 100-110 degrees C; drying for 220-260 minutes; taking out; and putting the product into a drying container to naturally cool.