NOVELTY - Preparation of solid alkali catalyst for preparing biodiesel comprises: (i) preparing modified attapulgite by drying natural attapulgite sample, grinding into a powder, adding hydrochloric acid, heating, reacting at a constant temperature, filtering, washing until the pH is neutral and vacuum drying; (ii) weighing modified attapulgite, adding sodium potassium tartrate in a beaker, adding deionized water to dissolve, impregnating modified attapulgite at room temperature, placing in an oven, aging, milling the mixture uniformly, placing in a muffle furnace to obtain the solid alkali catalyst.    USE - The catalyst is useful for the preparation of biodiesel (claimed).    ADVANTAGE - The catalyst has a simple preparation, high catalyzing efficiency and good stability. The biodiesel: is easily separated from the catalyst, reduces the height of the device and device corrosion degree, reduces the reaction steps and industrial waste water, thus reducing the production cost, in comparison to the biodiesel obtained from the conventional catalysts.    DETAILED DESCRIPTION - Preparation of a solid alkali catalyst for preparing biodiesel comprises: (i) preparing modified attapulgite by drying natural attapulgite sample, grinding into a powder, weighing the powder, adding 2 mol/l hydrochloric acid to the powder, where the solid-liquid ratio is 1:4 g/ml, heating to 100 degrees C, reacting at a constant temperature for 100 minutes, filtering, washing until the pH is neutral, vacuum drying at 100 degrees C for 12 hours and placing in a dryer; (ii) weighing modified attapulgite from the step (i), adding sodium potassium tartrate in a beaker as a carrier, adding deionized water to dissolve, impregnating modified attapulgite at room temperature for 12 hours, placing in an oven at 100 degrees C, aging for 12 hours, milling the mixture uniformly, placing for 5 hours in a muffle furnace and calcining at 300-800 degrees C to obtain the solid alkali catalyst, where the molar ratio of sodium potassium tartrate and modified attapulgite is 0.8:1-2.5:1; (iii) using the catalyst for preparing biodiesel by catalyzing method using a device, comprising a stirrer, a reflux condensing tube, a thermometer and a feeding device, adding soybean oil and methanol in a ratio of 1:1 g/ml and the solid alkali catalyst, which is 10 wt.% of the mass of soybean oil, in a 250 ml flask, raising the temperature to 60 degrees C to react for 2 hours, centrifuging and separating the reaction product, rotating and evaporating, removing the residual methanol, allowing to stand, separating and pouring out the upper layer oil phase to obtain biodiesel.