NOVELTY - Industrial preparation of biodiesel using waste oil i.e. peanut oil leftovers, waste oil of catering industry, and waste animal fat, comprises adding waste grease and solid acid catalyst, introducing gas-phase methanol while distilling a large amount of methanol, and carrying out esterification under the condition of replenishing methanol while stirring; carrying out ester exchange reaction with the liquid obtained by esterification, methanol, and solid-base alkali catalyst; and standing or centrifuging and separating the liquid.    USE - Industrial preparation of biodiesel for use in diesel engines, shipping, and fuel furnaces (claimed).    ADVANTAGE - The method provides biodiesel, which meets the national standard of number 0 diesel. It has low raw material cost, environment protection, and high product yield; is stable and suitable for mass production; and achieves stable and uniform product quality.    DETAILED DESCRIPTION - Industrial preparation of biodiesel using waste oil i.e. peanut oil leftovers, waste oil of catering industry, and waste animal fat, comprises:    (A) adding 98.5-9.0 wt.% waste grease and 1.0-1.5 wt.% solid acid catalyst to a reaction kettle; controlling the reaction temperature at 72-76 degrees C; introducing gas-phase methanol at normal pressure while distilling a large amount of methanol; carrying out esterification under the condition of replenishing methanol while stirring for 60-240 minutes; after stopping the reaction, standing; and discharging the acidic catalyst and impurities at the lower layer;    (B) putting 70-80 wt.% liquid obtained by esterification, 15-25 wt.% methanol, and 1-5 wt.% solid-base alkali catalyst to a reaction kettle; controlling the reaction temperature at 64-70 degrees C; stirring; and refluxing at normal pressure for 30-120 minutes to carry out ester exchange reaction; and    (C) after stopping ester exchange reaction, standing or centrifuging and separating the liquid, where upper layer is the prepared biodiesel and residual methanol and the lower layer includes glycerin and solid alkali catalyst; discharging the lower layer; separating the solid alkali; refining glycerin to obtain glycerin by-product; distilling the upper layer material; recycling the residual methanol; washing with water; and refining to obtain biodiesel.    An INDEPENDENT CLAIM is included for biodiesel obtained by the industrial preparation method using waste oil.